feat: update datetime handling to use UTC and improve type annotations

app/db/auth.py

@@ -1,5 +1,6 @@
-from datetime import datetime, timezone
-from typing import Any, Mapping
+from collections.abc import Mapping
+from datetime import UTC, datetime
+from typing import Any
 
 from core.mongodb import get_database
 from models.auth import AuthUserDocument
@@ -10,7 +11,7 @@ REVOKED_COLLECTION_NAME = "revoked_tokens"
 
 
 def utcnow() -> datetime:
-    return datetime.now(timezone.utc)
+    return datetime.now(UTC)
 
 
 async def users_collection() -> AsyncIOMotorCollection[dict[str, Any]]:

app/db/proxy.py

@@ -1,5 +1,6 @@
-from datetime import datetime, timezone
-from typing import Any, Mapping
+from collections.abc import Mapping
+from datetime import UTC, datetime
+from typing import Any
 
 from core.mongodb import get_database
 from models.proxy import ProxyDocument, ProxyUpdateInput
@@ -12,7 +13,7 @@ COLLECTION_NAME = "proxies"
 
 
 def _utcnow() -> datetime:
-    return datetime.now(timezone.utc)
+    return datetime.now(UTC)
 
 
 async def _collection() -> AsyncIOMotorCollection[dict[str, Any]]: