Cleaned up various files by removing unused or redundant import statements to improve code readability and reduce potential confusion. No functional changes were made.
Replaces the L2 cache layer's SQLite implementation with an async SQLAlchemy-based database model (CacheEntries). Updates cache_manager.py to use db_query and db_save for cache operations, adds semantic cache handling with ChromaDB, and introduces async cache clearing and expiration cleaning methods. Adds the CacheEntries model and integrates it into the database API.
