test(entity_stublib): ConfigFlow stub accepts the domain= __init_subclass__ kwarg and load_entity_modules drops config_flow (per-file loader ownership preserved) (completes P5-2 test scaffolding)

tests/entity_stublib.py

@@ -121,7 +121,16 @@ def install() -> None:
 
     config_entries = types.ModuleType("homeassistant.config_entries")
     config_entries.ConfigEntry = type("ConfigEntry", (), {})
-    config_entries.ConfigFlow = type("ConfigFlow", (), {})
+    _config_flow_base = type(
+        "ConfigFlow",
+        (),
+        {
+            "__init_subclass__": classmethod(
+                lambda cls, domain=None, **kwargs: None
+            ),
+        },
+    )
+    config_entries.ConfigFlow = _config_flow_base
     config_entries.OptionsFlow = type("OptionsFlow", (), {})
     sys.modules["homeassistant.config_entries"] = config_entries