Remove unused pub code from workspace

[charliermarsh]

Summary

This PR runs hawk over the uv codebase to:

1. Remove dead code (i.e., code marked as pub that isn't called by any other crates).
2. Reduce visibility of symbols (i.e., to make code non-pub if only called internally, etc.).

I skimmed through the changes and added exceptions where they felt warranted (to hawk.toml). I've included the hawk.toml file in the prior commit, but am excluding it from being committed, since it's not at a point that we have automated tooling.