- What I did
Made concurrent write access to the cache's index safe.

- How I did it

1. Centralized all write access to the cache's index.json into a single file
2. Added file locking utility using fcntl on Unix and Unix-like systems
3. Leveraged the file locking for cache writes

Ignored read locks for now, although the utility supports it. Too many places it could be added.

- How to verify it
CI to ensure no regressions, manual testing for lock timing.

- Description for the changelog

Concurrent access to writing index.json in cache