style: document cleanup now-capture and widen test sleep margin

tests/test_utils.py

@@ -81,9 +81,9 @@ class TestDataStoreCleanup:
 
     def test_cleanup_removes_expired_keeps_fresh(self):
         """Test that cleanup removes expired entries and keeps fresh ones."""
-        store = DataStore(max_age_seconds=0.001, name="test")
+        store = DataStore(max_age_seconds=0.05, name="test")
         store.set("old", 1)
-        time.sleep(0.01)
+        time.sleep(0.06)
         store.set("new", 2)
 
         removed = store.cleanup()

utils/cleanup.py

@@ -123,6 +123,7 @@ class DataStore:
         Returns:
             Number of entries removed
         """
+        # Capture now once so both the scan and re-validation use the same cutoff.
         now = time.time()
 
         with self._lock: