docs: def clean_history(self, widget, event=None):
          """Triggered when the 'Clean History' button is clicked.
  
          Empties the execution history tree by adjusting the start index and updates tree store and view.
          """
          self.history_tree_store.clear()
          selected_sm_m = self.model.get_selected_state_machine_model()
          if selected_sm_m:
              # the core may continue running without the GUI and for this it needs its execution histories
              if state_machine_execution_engine.finished_or_stopped():
                  selected_sm_m.state_machine.destroy_execution_histories()
                  self.update()