## Summary
The assumption that all tags are listed under a flat `.git/ref/tags`
structure was wrong. Git creates a hierarchy of directories for tags
containing slashes. To fix the cache key calculation, we need to
recursively traverse all files under that folder instead.
## Test Plan
1. Create an `uv` project with git-tag cache-keys;
2. Add any tag with slash;
3. Run `uv sync` and see uv_cache_info error in verbose log;
4. `uv sync` doesn't trigger reinstall on next tag addition or removal;
5. With fix applied, reinstall triggers on every tag update and there
are no errors in the log.
Fixes#10467
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Co-authored-by: Sergei Nizovtsev <sergei.nizovtsev@eqvilent.com>
Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>