fix: ruff findings

tests/test_pruning.py

@@ -5,7 +5,6 @@ day aggregates are retained indefinitely.
 
 Issue #74: Boundary anchors required for successor evidence are retained.
 """
-import sqlite3
 import sys
 from datetime import datetime, timezone, timedelta
 from pathlib import Path
@@ -124,7 +123,7 @@ class TestPruneOldSamples:
         _insert_sample(store_conn, "2026-09-16T12:30:00+00:00", 2000000)
         
         # Run pruning
-        pruned = prune_old_samples(store_conn, now, retention_days=14)
+        prune_old_samples(store_conn, now, retention_days=14)
         
         # The boundary anchor should be retained
         cursor = store_conn.execute(
@@ -148,7 +147,7 @@ class TestPruneOldSamples:
         store_conn.commit()
         
         # Run pruning
-        pruned = prune_old_samples(store_conn, now, retention_days=14)
+        prune_old_samples(store_conn, now, retention_days=14)
         
         # Keep the source samples until local-day replacement evidence exists.
         cursor = store_conn.execute(