chore: fix all ruff lint warnings

- Remove unused datetime imports from openbb_service, market_service,
  quantitative_service (now using obb_utils.days_ago)
- Remove unused variable 'maintains' in routes_sentiment
- Remove unused imports in test files
- Fix forward reference annotation in test helper

market_service.py

@@ -2,7 +2,6 @@
 
 import asyncio
 import logging
-from datetime import datetime, timezone, timedelta
 from typing import Any
 
 from openbb import obb