Track cython's Py_LIMITED_API support

[ap--]

I need to revisit compiling seabreeze with the limited API once these initial PRs get merged.

PRs: https://github.com/cython/cython/labels/limited%20api

• Get some of the limited API working with Py_LIMITED_API defined cython/cython#5550
• Avoid using Py_OptimizeFlag in the Limited API. cython/cython#5606
• Get some minimal cdef classes working with Py_LIMITED_API cython/cython#5617
• [BUG] Limited API bytes.decode fails cython/cython#5648
• [BUG] limited_api: for b in x generates unstable PyList_GET_SIZE and PySequence_ITEM cython/cython#5641
• Fix "except Exception" in limited api cython/cython#5699
• [BUG] classes with __weakref__ don't compile using the limited api cython/cython#5793
• Support weakref in limited api cdef classes cython/cython#5840
• [BUG] classmethods don't compile using the limited api cython/cython#5797
• Make classmethod work in limited-api cython/cython#5800

[ap--]

tested with Cython 3.0.1 and it didn't work yet.

[ap--]

With the compile-seabreeze branch here https://github.com/ap--/cython/tree/compile-seabreeze only the two issues above are missing (hopefully)

TODO: upstream the changes from my fork...

[ap--]

Compiling abi3 wheels for cp311 and above works with https://github.com/ap--/cython/tree/compile-seabreeze 🎉

(Merged the weakref and classmethod PRs and fixed two minor issues)