fix: ruff findings

src/fenris/repair.py

@@ -13,11 +13,11 @@ Contracts:
 """
 import logging
 import sqlite3
-from dataclasses import dataclass, field
+from dataclasses import dataclass
 from datetime import datetime, timedelta, timezone
 from typing import Optional, List, Tuple
 
-from .derive import find_previous_sample, derive_hours_from_interval, _parse_ts
+from .derive import derive_hours_from_interval, _parse_ts
 
 logger = logging.getLogger(__name__)