FEM: Purge tool deletes all result objects. Fixes #23028

- Correctly deletes children of pipeline without error on delete
- Ensures visualizations are also deleted as they are result objects too
- Ensures purge tool uses a transaction, like all tools should

src/Mod/Fem/femobjects/base_fempostvisualizations.py

@@ -80,6 +80,7 @@ class PostVisualization(base_fempythonobject.BaseFemPythonObject):
 
     def __init__(self, obj):
         super().__init__(obj)
+        self.Type = "Fem::FemPostVisualization"
         obj.addExtension("App::GroupExtensionPython")
         self._setup_properties(obj)