When the cache worker downloaded a package through the proxy, dependencies
were always queued with depth=0 instead of depth+1. This meant depth limits
weren't properly enforced for nested dependencies.
Changes:
- Add cache-depth query parameter to pypi_download_file endpoint
- Worker now passes its current depth when fetching packages
- Dependencies are queued at cache_depth+1 instead of hardcoded 0
- Add tests for depth tracking behavior
3bdeade7ca