fix: ruff findings

tests/test_preferences.py

@@ -10,11 +10,11 @@ Covers:
   - CLI status and collector behaviour unchanged by preferences
 """
 import json
+from datetime import datetime, timezone
 import os
 from pathlib import Path
 from unittest.mock import patch
 
-import pytest
 import sys
 
 sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
@@ -295,7 +295,3 @@ class TestCLIIsolation:
         tables_after = sorted(r[0] for r in cursor.fetchall())
         conn.close()
         assert tables_before == tables_after
-
-
-# Need datetime for CLI isolation test
-from datetime import datetime, timezone