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

routes_sentiment.py

@@ -76,7 +76,6 @@ async def stock_sentiment(symbol: str = Path(..., min_length=1, max_length=20)):
     if isinstance(upgrades_data, list) and upgrades_data:
         ups = sum(1 for u in upgrades_data if u.get("action") in ("up", "init"))
         downs = sum(1 for u in upgrades_data if u.get("action") == "down")
-        maintains = len(upgrades_data) - ups - downs
         if len(upgrades_data) > 0:
             upgrade_score = (ups - downs) / len(upgrades_data)
             scores.append(("upgrades", round(upgrade_score, 3), 0.20))