chore: use isConnected flag instead of checking db value.

Signed-off-by: xsahil03x <[email protected]>

packages/stream_chat/test/src/db/chat_persistence_client_test.dart

@@ -12,6 +12,9 @@ import 'package:stream_chat/src/db/chat_persistence_client.dart';
 import 'package:test/test.dart';
 
 class TestPersistenceClient extends ChatPersistenceClient {
+  @override
+  bool get isConnected => throw UnimplementedError();
+
   @override
   Future<void> connect(String userId) => throw UnimplementedError();