Revert changes to pyproject.toml when sync fails duing uv add

[tjquillan]

Summary

This is a attempt at fixing #6486. It reverts changes made to pyproject.toml when sync fails during uv add. This solution felt a little heavy handed and could probably be improved but it is what happens when locking fails during uv add so I thought it would be a good start.

Test Plan

I have added a test case for this to tests/edit.rs. It uses pytorch==1.0.2 to achieve the desired failure.

[charliermarsh]

Thanks, this looks good! Feel free to un-mark as draft.

[charliermarsh]

I can fix that test failure -- or you can add this:

    let filters = std::iter::once((r"exit code: 1", "exit status: 1"))
        .chain(context.filters())
        .collect::<Vec<_>>();
    uv_snapshot!(filters, ...)

[charliermarsh]

Thank you!