code: @MainThread
      @ObjectiveCName("subscribeWithListener:")
      public void subscribe(@NotNull ModelChangedListener<UserVM> listener) {
          // Runtime.checkMainThread();
          if (listeners.contains(listener)) {
              return;
          }
          listeners.add(listener);
          listener.onChanged(this);
      }
docs: Subscribe to UserVM updates
  
  @param listener UserVM changed listener