## Summary
We currently accept `--index-url /path/to/index` on the command line,
but confusingly, not in `requirements.txt`. This PR just brings the two
in sync.
## Test Plan
New snapshot tests.
## Summary
It turns out that `normalize_path` (sourced from Cargo) has a subtle
bug. If you pass it a relative path that traverses beyond the root, it
silently drops components. So, e.g., passing `../foo/bar`, it will just
drop the leading `..` and return `foo/bar`.
This PR encodes that behavior as a `Result` and avoids using it in such
cases.
Closes https://github.com/astral-sh/uv/issues/3012.