feat(connectors): add AsyncDBConnectorProtocol; implement on PostgreSQL and SQLite

pytest.ini

@@ -4,6 +4,7 @@ python_files = test_*.py
 python_classes = Test*
 python_functions = test_*
 addopts = -v
+asyncio_default_fixture_loop_scope = function
 pythonpath = src
 markers =
     postgres: mark test as requiring a live PostgreSQL instance

src/orcapod/databases/__init__.py

@@ -25,6 +25,12 @@
 #   PostgreSQLConnector  -- PLT-1075 (psycopg3)                          ✓
 #   SpiralDBConnector    -- PLT-1074
 #
+# Connectors that also implement AsyncDBConnectorProtocol:
+#
+#   PostgreSQLConnector  -- native psycopg3 async (PLT-1453)              ✓
+#   SQLiteConnector      -- asyncio.to_thread() wrappers (PLT-1453)       ✓
+#   SpiralDBConnector    -- deferred to PLT-1456
+#
 # ArrowDatabaseProtocol backends (existing, not connector-based):
 #
 #   DeltaTableDatabase    -- Delta Lake (deltalake package)