fix: access thrift backend through session

Author: varun-edachali-dbx

tests/e2e/test_driver.py

@@ -916,7 +916,7 @@ def test_cursor_error_handling(self):
             assert op_handle is not None
 
             # Manually close the operation to simulate server-side closure
-            conn.thrift_backend.close_command(op_handle)
+            conn.session.thrift_backend.close_command(op_handle)
 
             cursor.close()