Add a garbage collection mechanism to the CLI (#1217)
## Summary
Detects unused cache entries, which can come in a few forms:
1. Directories that are out-dated via our versioning scheme.
2. Old source distribution builds (i.e., we have a more recent version).
3. Old wheels (stored in `archive-v0`, but not symlinked-to from
anywhere in the cache).
Closes https://github.com/astral-sh/puffin/issues/1059.
