Called when the state's IStateView.Root is detached from its UI panel.
Fires whenever the visual element receives a DetachFromPanelEvent. Like StateView<T0>.OnViewAttached, this can fire multiple times in a state's lifetime (tab switches, and so on), and a matching StateView<T0>.OnViewAttached may follow. Use this callback to release resources tied to panel presence, such as event subscriptions or scheduled tasks.