Refactor code structure for improved readability and maintainability

app/core/database.py

@@ -25,7 +25,7 @@ engine: AsyncEngine = create_async_engine(
 )
 
 
-async def get_db() -> AsyncGenerator[AsyncSession, None]:
+async def get_db() -> AsyncGenerator[AsyncSession]:
     """Get a database session for dependency injection."""
     logger = get_logger(__name__)
     async with AsyncSession(engine) as session:

app/main.py

@@ -17,7 +17,7 @@ from app.services.socket import socket_manager
 
 
 @asynccontextmanager
-async def lifespan(_app: FastAPI) -> AsyncGenerator[None, None]:
+async def lifespan(_app: FastAPI) -> AsyncGenerator[None]:
     """Application lifespan context manager for setup and teardown."""
     setup_logging()
     logger = get_logger(__name__)