Sync the code here with upstream numpy/numpy

[mattip]

I think the code here is in danger of getting out of sync with upstream. For instance, the requirements files for openblas use different versions, and I think the cibuildwheel.toml is not used upstream. It would be nice to

• use the same files here as upstream
• have a CI check that the files are the same

or

• actually use the upstream files here too

[rgommers]

actually use the upstream files here too

The other way around actually: use these files from the main numpy/numpy repo. But yeah point taken. I'd like to clean up the main repo asap, let me try to open a PR with what I have before signing off. And then we can check for remaining duplication & things that could go out of sync.

[rgommers]

90% of this was done in numpy/numpy#29540. There is a minor amount of overlap left, would be nice to look at that with fresh eyes again in a little while and see if that's fine as is or could use some tweaks. Not urgent.

[rgommers]

Looking at this again, I think the main change that could be made is to use the cibuildwheel.toml from this repo in the main repo, and remove the independent cibuildwheel content in pyproject.toml and cibw_*.sh there.