Normalize relative paths when `--project` is specified (#9709)
## Summary
In the end, the problem is that `relative_to` has incorrect behavior if
either path is non-normalize (e.g., `foo/bar/../project`). So I've fixed
that method, but we _also_ now normalize `project` upfront, which _also_
fixes the issue.
Closes https://github.com/astral-sh/uv/issues/9692.
