fix: ruff findings

tests/test_issue_77.py

@@ -6,7 +6,6 @@ These tests verify that:
 3. Edge cases like zero-delta intervals and unknown daily shares are handled
 4. qualifying_days_progress shows honest qualifying day count
 """
-import sqlite3
 from datetime import datetime, timedelta, timezone
 from pathlib import Path
 
@@ -15,10 +14,9 @@ import sys
 sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
 
 from fenris.store import init_store
-from fenris.monitoring_periods import ensure_period_open, close_period
+from fenris.monitoring_periods import ensure_period_open
 from fenris.projection import (
-    compute_projection, ConfidenceState, BaselineTier,
-    WARMING_MIN_DAYS, WARMING_COVERAGE_FLOOR, WARMING_MAX_LOW_COVERAGE,
+    compute_projection, ConfidenceState,
 )