Refactor database module and add testing utilities

Simplify database module by re-organizing engine creation, session handling, and removing redundant methods. Introduce SQLite compatibility for testing and add a utility module for test database setup and teardown. Integrate initial unit tests for user models and update dependencies for security and testing.

backend/app/core/config.py

@@ -14,7 +14,16 @@ class Settings(BaseSettings):
     POSTGRES_PORT: str = "5432"
     POSTGRES_DB: str = "eventspace"
     DATABASE_URL: Optional[str] = None
+    db_pool_size: int = 20  # Default connection pool size
+    db_max_overflow: int = 50  # Maximum overflow connections
+    db_pool_timeout: int = 30  # Seconds to wait for a connection
+    db_pool_recycle: int = 3600  # Recycle connections after 1 hour
 
+    # SQL debugging (disable in production)
+    sql_echo: bool = False  # Log SQL statements
+    sql_echo_pool: bool = False  # Log connection pool events
+    sql_echo_timing: bool = False  # Log query execution times
+    slow_query_threshold: float = 0.5  # Log queries taking longer than this
     @property
     def database_url(self) -> str:
         """