Avoid always rebuilding dynamic metadata (#5206)
## Summary
I don't think that "always reinstall" is tenable for `uv run`. My
perspective on this is that if you want "always reinstall", you can now
set it persistently in your `pyproject.toml` or `uv.toml`.
As a smaller change, we could instead disable this _only_ for the
Project API.
Closes https://github.com/astral-sh/uv/issues/4946.
