add timeline pkg to flutter

packages/z-timeline/lib/bridge.dart

@@ -0,0 +1,37 @@
+import 'dart:convert';
+import 'dart:js_interop';
+
+@JS('window.__zendegi__')
+external _ZendegiBridge? get _bridge;
+
+extension type _ZendegiBridge._(JSObject _) implements JSObject {
+  external JSString getState();
+  external void onEvent(JSString json);
+  external set updateState(JSFunction callback);
+}
+
+Map<String, dynamic>? readInitialState() {
+  final bridge = _bridge;
+  if (bridge == null) return null;
+  final json = bridge.getState().toDart;
+  return jsonDecode(json) as Map<String, dynamic>;
+}
+
+void onStateUpdated(void Function(Map<String, dynamic> state) callback) {
+  final bridge = _bridge;
+  if (bridge == null) return;
+  bridge.updateState = ((JSString json) {
+    final decoded = jsonDecode(json.toDart) as Map<String, dynamic>;
+    callback(decoded);
+  }).toJS;
+}
+
+void emitEvent(String type, [Map<String, dynamic>? payload]) {
+  final bridge = _bridge;
+  if (bridge == null) return;
+  final event = <String, dynamic>{'type': type};
+  if (payload != null) {
+    event['payload'] = payload;
+  }
+  bridge.onEvent(jsonEncode(event).toJS);
+}