Skip metadata fetch for `--no-deps` and `pip sync` (#7127)
## Summary
I think a better tradeoff here is to skip fetching metadata, even though
we can't validate the extras.
It will help with situations like
https://github.com/astral-sh/uv/issues/5073#issuecomment-2334235588 in
which, otherwise, we have to download the wheels twice.
