fix: ruff findings

tests/test_legacy_migration.py

@@ -4,9 +4,6 @@ Tests the idempotent, interruption-safe import of history.jsonl into the
 observation store.
 """
 import json
-import os
-import sqlite3
-import tempfile
 from datetime import datetime, timezone
 from pathlib import Path
 from typing import Any, Dict
@@ -17,7 +14,7 @@ import pytest
 import sys
 sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
 
-from fenris.legacy import import_legacy_history, is_legacy_imported, _parse_history_line
+from fenris.legacy import import_legacy_history, _parse_history_line
 from fenris.store import init_store