Add Polly resilience policies

clients/dotnet/MxGateway.Client.Tests/FakeGatewayTransport.cs

@@ -36,11 +36,22 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.Ok },
     };
 
+    public Queue<Exception> OpenSessionExceptions { get; } = new();
+
+    public Queue<Exception> CloseSessionExceptions { get; } = new();
+
+    public Queue<Exception> InvokeExceptions { get; } = new();
+
     public Task<OpenSessionReply> OpenSessionAsync(
         OpenSessionRequest request,
         CallOptions callOptions)
     {
         OpenSessionCalls.Add((request, callOptions));
+        if (OpenSessionExceptions.TryDequeue(out Exception? exception))
+        {
+            throw exception;
+        }
+
         return Task.FromResult(OpenSessionReply);
     }
 
@@ -49,6 +60,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         CallOptions callOptions)
     {
         CloseSessionCalls.Add((request, callOptions));
+        if (CloseSessionExceptions.TryDequeue(out Exception? exception))
+        {
+            throw exception;
+        }
+
         return Task.FromResult(CloseSessionReply);
     }
 
@@ -57,6 +73,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         CallOptions callOptions)
     {
         InvokeCalls.Add((request, callOptions));
+        if (InvokeExceptions.TryDequeue(out Exception? exception))
+        {
+            throw exception;
+        }
+
         return Task.FromResult(_invokeReplies.Dequeue());
     }