fix offline user connection, add tests

Signed-off-by: Sahil Kumar <[email protected]>

packages/stream_chat/lib/src/client/client.dart

@@ -289,7 +289,7 @@ class StreamChatClient {
       final event = await openConnection();
       return event;
     } catch (e, stk) {
-      if (e is StreamChatNetworkError && e.isRetriable) {
+      if (e is StreamWebSocketError && e.isRetriable) {
         final event = await _chatPersistenceClient?.getConnectionInfo();
         if (event != null) return event;
       }

packages/stream_chat/lib/src/core/error/stream_chat_error.dart

@@ -45,6 +45,9 @@ class StreamWebSocketError extends StreamChatError {
   /// Response body. please refer to [ErrorResponse].
   final ErrorResponse? data;
 
+  ///
+  bool get isRetriable => data == null;
+
   @override
   List<Object?> get props => [...super.props, code];