fix: CancelListenFunc should have a declared return type (#908)

`CancelListenFunc` should have a declared return type, otherwise
`dynamic` will start trickling into the users' of this code bases.

Author: spydon

lib/src/data_stream/stream_writer.dart

@@ -11,7 +11,7 @@ import '../utils.dart';
 
 class BaseStreamWriter<T, InfoType extends BaseStreamInfo> {
   final StreamWriter<T> writableStream;
-  Function()? onClose;
+  Future<void> Function()? onClose;
 
   final InfoType info;
 
@@ -23,7 +23,7 @@ class BaseStreamWriter<T, InfoType extends BaseStreamInfo> {
 
   Future<void> close() async {
     await writableStream.close();
-    onClose?.call();
+    await onClose?.call();
   }
 }
 

lib/src/managers/event.dart

@@ -185,7 +185,7 @@ abstract class EventsListenable<T> extends Disposable {
       // cast to E
       await then(event);
       // cancel after 1 event
-      cancelFunc?.call();
+      await cancelFunc?.call();
     });
     return cancelFunc;
   }

lib/src/participant/local.dart

@@ -1218,13 +1218,7 @@ extension DataStreamParticipantMethods on LocalParticipant {
 
     final cancelFun = room.engine.events.once<EngineClosingEvent>((_) => onEngineClose);
 
-    final writer = TextStreamWriter(
-      writableStream: writableStream,
-      info: info,
-      onClose: () {
-        cancelFun?.call();
-      },
-    );
+    final writer = TextStreamWriter(writableStream: writableStream, info: info, onClose: cancelFun);
 
     return writer;
   }
@@ -1320,9 +1314,7 @@ extension DataStreamParticipantMethods on LocalParticipant {
     final byteWriter = ByteStreamWriter(
       writableStream: writableStream,
       info: info,
-      onClose: () {
-        cancelFun?.call();
-      },
+      onClose: cancelFun,
     );
 
     return byteWriter;

lib/src/preconnect/pre_connect_audio_buffer.dart

@@ -223,7 +223,7 @@ class PreConnectAudioBuffer {
   Future<void> reset() async {
     await stopRecording();
     _timeoutTimer?.cancel();
-    _participantStateListener?.call();
+    await _participantStateListener?.call();
     _participantStateListener = null;
     _buffer.clear();
 

lib/src/types/other.dart

@@ -19,7 +19,7 @@ import 'package:flutter/material.dart';
 import '../extensions.dart';
 import '../participant/participant.dart';
 
-typedef CancelListenFunc = Function();
+typedef CancelListenFunc = Future<void> Function();
 
 /// Protocol version to use when connecting to server.
 /// Usually it's not recommended to change this.

test/core/room_e2e_test.dart

@@ -87,7 +87,7 @@ void main() {
       await room.events.waitFor<ParticipantConnectedEvent>(duration: const Duration(seconds: 1));
 
       // Clean up listener
-      cancel();
+      await cancel();
 
       // Verify participant had tracks when connected event was emitted
       expect(participantHadTracksOnConnect, isTrue,