COMPAT: cpow=True for Cython >= 3.0 compatibility

[ChadFulton]

• closes Compilation failures with Cython 3.0 #8868
• tests passed.
• code/documentation is well formatted.
• properly formatted commit message.

These relatively minor changes allowed local compilation with Python 3.11 / Cython 3.0.0. Will be interesting to see if CI passes.

[hroncok]

I am testing this in Fedora and I've noticed a lot of:

performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:83:5: Exception check on 'shamilton_filter_log_iteration' will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:231:5: Exception check on 'dhamilton_filter_log_iteration' will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:379:5: Exception check on 'chamilton_filter_log_iteration' will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:527:5: Exception check on 'zhamilton_filter_log_iteration' will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:71:42: Exception check will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:219:42: Exception check will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:362:32: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:365:26: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:367:42: Exception check will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:425:22: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:428:18: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:451:14: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:452:41: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:510:32: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:513:26: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:515:42: Exception check will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:573:22: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:576:18: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:599:14: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_hamilton_filter.pyx:600:41: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:56:5: Exception check on 'skim_smoother_log_iteration' will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:155:5: Exception check on 'dkim_smoother_log_iteration' will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:254:5: Exception check on 'ckim_smoother_log_iteration' will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:353:5: Exception check on 'zkim_smoother_log_iteration' will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:46:39: Exception check will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:145:39: Exception check will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:244:39: Exception check will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:312:20: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:315:18: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:343:39: Exception check will always require the GIL to be acquired.
Possible solutions:
	1. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
	2. Use an 'int' return type on the function to allow an error code to be returned.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:411:20: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
performance hint: statsmodels/tsa/regime_switching/_kim_smoother.pyx:414:18: Exception check will always require the GIL to be acquired. Declare the function as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.

Seem like this is worth considering before switching to cython 3.

[bashtage]

These are all fixed in the main branch, and will be out in the next release.

[hroncok]

I see, in #9078