BLD: stop building win32

[andyfaff]

In #43 there was mention about dropping win32. This PR would carrry that out. PR marked as draft so it's not accidentally merged before a full decision.

[rgommers]

This was discussed on the mailing list a month ago, and there were no objections: thread link. I think we can go ahead and merge this - @charris do you agree?

[charris]

Fine with me. I was letting it sit until we figured out the pytest warnings, but that now seems well in hand with the Python 3.15 builds in NumPy that we can use to track them.

[charris]

@andyfaff Remember to move windows 32 bits to tier 3 in doc/neps/nep-0057-numpy-platform-support.rst.

[andyfaff]

I can move it to tier 3, but it needs a maintainer to commit to keeping CI working in numpy/numpy. I don't mind tending to CI files, but I don't have the capacity to go deeper than that at the moment. @ngoldbaum, do you mind if I add you to that file?

[ngoldbaum]

Sure, it's nice having a 32bit free-threaded CI target. Or it will be once my PR adding that is merged.

[charris]

Thanks @andyfaff .