generics instead of covariant implementing for TrackPublication

lib/src/publication/local_track_publication.dart

@@ -6,10 +6,7 @@ import '../proto/livekit_models.pb.dart' as lk_models;
 import '../track/local.dart';
 import 'track_publication.dart';
 
-class LocalTrackPublication<T extends LocalTrack> extends TrackPublication {
-  @override
-  covariant T? track;
-
+class LocalTrackPublication<T extends LocalTrack> extends TrackPublication<T> {
   @override
   final LocalParticipant participant;
 
@@ -27,7 +24,7 @@ class LocalTrackPublication<T extends LocalTrack> extends TrackPublication {
   }
 
   @override
-  Future<bool> updateTrack(covariant T? newValue) async {
+  Future<bool> updateTrack(T? newValue) async {
     final didUpdate = await super.updateTrack(newValue);
 
     if (newValue != null) {

lib/src/publication/remote_track_publication.dart

@@ -30,10 +30,8 @@ class RendererVisibility {
 
 /// Represents a track publication from a RemoteParticipant. Provides methods to
 /// control if we should subscribe to the track, and its quality (for video).
-class RemoteTrackPublication<T extends RemoteTrack> extends TrackPublication {
-  @override
-  covariant T? track;
-
+class RemoteTrackPublication<T extends RemoteTrack>
+    extends TrackPublication<T> {
   @override
   final RemoteParticipant participant;
 

lib/src/publication/track_publication.dart

@@ -13,16 +13,16 @@ import '../types.dart';
 /// Base for [RemoteTrackPublication] and [LocalTrackPublication],
 /// can not be instantiated directly.
 
-abstract class TrackPublication extends Disposable {
+abstract class TrackPublication<T extends Track> extends Disposable {
   final String sid;
   final String name;
   final lk_models.TrackType kind;
   final TrackSource source;
 
-  // Relevant type must be implemented
-  abstract Track? track;
+  /// The current [Track] for this publication (readonly).
+  T? get track => _track;
+  T? _track;
 
-  // Relevant type must be implemented
   /// The [Participant] this publication belongs to.
   abstract final Participant participant;
 
@@ -71,11 +71,11 @@ abstract class TrackPublication extends Disposable {
   // Returns true if value has changed.
   // Intended for internal use only.
   @internal
-  Future<bool> updateTrack(Track? newValue) async {
-    if (track == newValue) return false;
+  Future<bool> updateTrack(T? newValue) async {
+    if (_track == newValue) return false;
     // dispose previous track (if exists)
-    await track?.dispose();
-    track = newValue;
+    await _track?.dispose();
+    _track = newValue;
     return true;
   }
 }