feat: add dispose notifier to editor state

example/lib/pages/desktop_editor.dart

@@ -39,6 +39,14 @@ class _DesktopEditorState extends State<DesktopEditor> {
     commandShortcuts = _buildCommandShortcuts();
   }
 
+  @override
+  void dispose() {
+    editorScrollController.dispose();
+    editorState.dispose();
+
+    super.dispose();
+  }
+
   @override
   void reassemble() {
     super.reassemble();

lib/src/editor/find_replace_menu/find_menu_service.dart

@@ -36,6 +36,8 @@ class FindReplaceMenu implements FindReplaceService {
       editorState.service.scrollService?.enable();
     }
 
+    editorState.onDispose.removeListener(dismiss);
+
     _findReplaceMenuEntry?.remove();
     _findReplaceMenuEntry = null;
 
@@ -59,6 +61,8 @@ class FindReplaceMenu implements FindReplaceService {
       return;
     }
 
+    editorState.onDispose.addListener(dismiss);
+
     _findReplaceMenuEntry = OverlayEntry(
       builder: (context) {
         return Positioned(

lib/src/editor_state.dart

@@ -216,6 +216,16 @@ class EditorState {
   Timer? _debouncedSealHistoryItemTimer;
   final bool _enableCheckIntegrity = false;
 
+  // the value of the notifier is meaningless, just for triggering the callbacks.
+  final ValueNotifier<int> onDispose = ValueNotifier(0);
+
+  void dispose() {
+    _observer.close();
+    _debouncedSealHistoryItemTimer?.cancel();
+    onDispose.value += 1;
+    onDispose.dispose();
+  }
+
   /// Apply the transaction to the state.
   ///
   /// The options can be used to determine whether the editor