feat: option to build directly with uv

[henryiii]

Adding an option to build directly with uv. Will conflict with #2321, so probably will rebase after that one.

[jake-arkinstall]

I have a question on this.

UV supports workspaces, and a 'uv build' of a workspace may result in more than one wheel. I currently have a project which builds ~10 wheels per target platform, and I'd love to be able to do this with a single invocation of CIBuildWheel. Is that something that could be made possible (or something that is already possible)?

The reason I'm asking is that I haven't been able to get build[uv] to be able to work with uv workspace projects, but invoking uv directly could make that possible.

[henryiii]

That's interesting, probably! We might/will need to handle pure-Python output wheels, but other than that I think it should work. Nice to know this will enable something (especially since it's been annoying to make work due to astral-sh/uv#12639). I'll try to test that.

[henryiii]

I'm happy to push this off to 3.1 for now in interests of getting a 3.0 out. This is just a new option, not a change.