feat: Forward leave reason of disconnected events. (#250)

* feat: Forward leave reason of disconnected events.

* fix analyze.

* chore: print room disconnect reason when event.reason != null.

* chore: rename InternalDisconnectReason => ClientDisconnectReason.

example/lib/pages/room.dart

@@ -54,7 +54,10 @@ class _RoomPageState extends State<RoomPage> {
   }
 
   void _setUpListeners() => _listener
-    ..on<RoomDisconnectedEvent>((_) async {
+    ..on<RoomDisconnectedEvent>((event) async {
+      if (event.reason != null) {
+        print('Room disconnected: reason => ${event.reason}');
+      }
       WidgetsBindingCompatible.instance
           ?.addPostFrameCallback((timeStamp) => Navigator.pop(context));
     })