appending to a list now also triggers _notify_change_start

This helps in understanding if the list entries being added are "changing" themselves. Properties within
the added objects will trigger property changes when they are serialized, so we have to tell the observer
that he should not listen to them.

src/pydase/observer_pattern/observable/observable_object.py

@@ -148,6 +148,7 @@ class _ObservableList(ObservableObject, list[Any]):
         self._notify_changed(f"[{key}]", value)
 
     def append(self, __object: Any) -> None:
+        self._notify_change_start("")
         self._initialise_new_objects(f"[{len(self)}]", __object)
         super().append(__object)
         self._notify_changed("", self)