fix: Resolve Ruff E402 warnings and clean up imports across multiple modules

middleware/metrics.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 import time
 from typing import Callable
 
-from fastapi import BackgroundTasks, Request, Response
+from fastapi import Request, Response
 from starlette.middleware.base import BaseHTTPMiddleware
 
 from monitoring.metrics import observe_request