Add a comment on a fixture

Author: gwaramadze

tests/test_quixstreams/test_state/test_rocksdb/test_timestamped.py

@@ -11,6 +11,9 @@
 
 @pytest.fixture
 def store_type():
+    # This fixture is indirectly used by the `store_factory` fixture.
+    # Full dependency chain is:
+    # `store_type` -> `store_factory` -> `store` -> `transaction`
     return TimestampedStore