MNT: Build wheels with limited API

[effigies]

Inspired by @vstinner's PyCon slides, I wanted to see if we could build to the Python limited API, which allows a single wheel to support all versions of Python above some minimum.

I've collapsed the build matrix down, and added a broad test matrix to ensure that the built wheels work correctly. This will produce fewer wheels (one per-platform) that should be installable on Python 3.13 as soon as Numpy has a build out.

Once this is in, I can stop pestering you with updates to the build system.

I'm using https://github.com/joerick/python-abi3-package-sample/ as a guide.

[arokem]

I have to say that I am not 100% sure what's going on here. Is there any reason you can see not to merge this?

[effigies]

I had another look at this, and I think the tests may be passing because of the fallback version of tridisolve, and not because we can successfully compile this to the ABI. Closing for now.