Replace Mediator with Messenger

Toolkit.Foundation/AsyncResponseEventArgs.cs

@@ -0,0 +1,11 @@
+using CommunityToolkit.Mvvm.Messaging.Messages;
+
+namespace Toolkit.Foundation;
+
+public class AsyncResponseEventArgs<TMessage, TResponse> :
+    AsyncRequestMessage<TResponse>
+{
+    public TMessage? Message { get; set; }
+
+    public CancellationToken CancellationToken { get; set; }
+}