Omit dynamic versions from the lockfile (#10622)
## Summary
This PR modifies the lockfile to omit versions for source trees that use
`dynamic` versioning, thereby enabling projects to use dynamic
versioning with `uv.lock`.
Prior to this change, dynamic versioning was largely incompatible with
locking, especially for popular tools like `setuptools_scm` -- in that
case, every commit bumps the version, so every commit invalidates the
committed lockfile.
Closes https://github.com/astral-sh/uv/issues/7533.
