Support build constraints

[blueraft]

Summary

Partially resolves #5561. Haven't added overrides support yet but I can add it tomorrow if the current approach for constraints is ok.

Test Plan

cargo test

Manually checked trace logs after changing the constraints.

[blueraft]

I wasn't sure how to check if the built constraints were being respected for the compatible versions - this just check if the package gets resolved correctly.

[T-256]

isn't there anything via verbose flag?

[blueraft]

It's there in the verbose logs, but I don't know if we should use the verbose logs for snapshot tests.

[charliermarsh]

Thanks! Will review.

[paveldikov]

Does uv pip compile now include build dependencies in its output? Or do --build-constraints files have to be generated separately (how?)

[charliermarsh]

I don't believe this PR adds any way to lock the build resolution, only to constrain it, but we want to add that to uv.lock eventually.

[blueraft]

Related issue #5190

[hauntsaninja]

Not using UV_CONSTRAINT for build constraints should probably listed in the pip compatibility docs. Something like:

For constraining build time dependencies:

• pip lets you use PIP_CONSTRAINT environment variable to point to a constraints file. There is no CLI argument
• uv lets you use UV_BUILD_CONSTRAINT environment variable or a --build-constraint CLI argument

[charliermarsh]

Makes sense, good call @hauntsaninja.

[charliermarsh]

This overall looks good but I have to find a way to fix the stack size issues on Windows (nothing wrong with the PR specifically, it's an ongoing problem) -- and update the docs.