Video optimizations (#18)

* use events for `VideoTrackRenderer`

* logger

* implemented visibility detection

* optimize code with 1 param debounce func

* stop pending visibility event when disposed

* clean up

* mark internal

* report to track

* call dispose on pub and track

* use internal events to receive visibility events

* clean up visibility for disposed track

* listen to track visibility events on pub

* re-design

* quickly re-enable

* clean up

* clean up

lib/src/track/track.dart

@@ -3,15 +3,19 @@ import 'package:flutter_webrtc/flutter_webrtc.dart' as rtc;
 import 'package:meta/meta.dart';
 import 'package:uuid/uuid.dart';
 
+import '../events.dart';
 import '../extensions.dart';
 import '../logger.dart';
+import '../managers/event.dart';
 import '../proto/livekit_models.pb.dart' as lk_models;
 import '../support/disposable.dart';
 
 /// Wrapper around a MediaStreamTrack with additional metadata.
 /// Base for [AudioTrack] and [VideoTrack],
 /// can not be instantiated directly.
-abstract class Track extends DisposableChangeNotifier {
+abstract class Track extends DisposableChangeNotifier
+    with EventsEmittable<TrackEvent> {
+  static const uuid = Uuid();
   static const cameraName = 'camera';
   static const screenShareName = 'screen';
 
@@ -31,7 +35,13 @@ abstract class Track extends DisposableChangeNotifier {
     this.kind,
     this.name,
     this.mediaStreamTrack,
-  );
+  ) {
+    onDispose(() async {
+      logger.fine('${objectId} onDispose()');
+      // dispose events
+      await events.dispose();
+    });
+  }
 
   bool get muted =>
       mediaStreamTrack.muted == null ? false : mediaStreamTrack.muted!;
@@ -52,7 +62,6 @@ abstract class Track extends DisposableChangeNotifier {
     var cid = _cid ?? mediaStreamTrack.id;
 
     if (cid == null) {
-      const uuid = Uuid();
       cid = uuid.v4();
       _cid = cid;
     }