DOC: Fix refguide check script

[mtsokol]

Addresses: #25365

This PR enables running doctests on all docstrings (some docstrings had to be adjusted).

[mtsokol]

Now --doctests runs for all non-legacy public modules:

Running checks for 24 modules:
numpy.f2py ....
numpy.linalg ........................................................
numpy.lib .......
numpy.lib.format ...
numpy.lib.mixins ...
numpy.lib.recfunctions .......................
numpy.lib.scimath ....................
numpy.lib.stride_tricks ....
numpy.lib.npyio ...
numpy.lib.introspect ...
numpy.lib.array_utils .....
numpy.fft ....................
numpy.ma ..................................................................................................................................................................................................................................
numpy.polynomial .........
numpy.polynomial.chebyshev ......................................................................
numpy.polynomial.hermite ................................................................
numpy.polynomial.hermite_e ................................................................
numpy.polynomial.laguerre ................................................................
numpy.polynomial.legendre ...............................................................
numpy.polynomial.polynomial ..........................................................
numpy.matrixlib .....
numpy.random .........................................................
numpy.testing .............................................
numpy ..........................................................................................................................................................................................................................Warning: overflow encountered in scalar multiply
.........................................................................................................................................................................................................................................................................

OK: all checks passed!

[rgommers]

Looks good overall, thanks @mtsokol. Please consider taking over the most recent commit on https://github.com/rgommers/numpy/tree/docs-fix-refguide-check; the added # may vary markers make --doctests pass for me.

[charris]

Thanks @mtsokol .