ENH: Add armv7l wheel (manylinux/musllinux)

[Lauszus]

This PR add support for building wheels for armv7l

Note I used Claude Sonnet 4.6 to figure out the OpenBLAS overrides.

[andyfaff]

Please raise this request for new wheel platforms as a new issue on the numpy/numpy repository, or on the numpy-discussion mailing list. The discussion revolves around how popular the target will be, ease of creating wheels performing CI, etc.

[rgommers]

Hi @Lauszus, this isn't the place to start. Can you please read https://numpy.org/neps/nep-0057-numpy-platform-support.html and then open a feature request on the main numpy/numpy repo with a lot more context about the use cases and envisioned support?

I'll note that we have regular 32-bit Arm support since about a year (see numpy/numpy#28653), but that was nontrivial and I'm not sure it covers everything - reviewing regular CI coverage would be a good start.

[Lauszus]

Note I will revert this before potentially merging this

[Lauszus]

I have now opened up an issue: numpy/numpy#31351