Remove and reorder unused imports across the project for cleaner and more consistent code structure

backend/app/utils/test_utils.py

@@ -1,7 +1,8 @@
 import logging
-from sqlalchemy import create_engine, event
+
+from sqlalchemy import create_engine
 from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
-from sqlalchemy.orm import sessionmaker, clear_mappers
+from sqlalchemy.orm import sessionmaker
 from sqlalchemy.pool import StaticPool
 
 from app.core.database import Base