Remove xunit package source and test mock implementation per review feedback

Co-authored-by: drewnoakes <350947+drewnoakes@users.noreply.github.com>

Author: Copilot

NuGet.Config

@@ -2,9 +2,5 @@
 <configuration>
   <packageSources>
     <add key="NuGet.org" value="https://api.nuget.org/v3/index.json" />
-    <add key="xunit" value="https://www.myget.org/F/xunit/api/v3/index.json" />
   </packageSources>
-  <disabledPackageSources>
-    <add key="xunit" value="true" />
-  </disabledPackageSources>
 </configuration>

src/NetMQ.Tests/NetMQMonitorTests.cs

@@ -188,86 +188,5 @@ public void ConvertArgThrowsForInvalidType()
             MonitorEvent monitorEvent = new MonitorEvent(SocketEvents.All, addr: "", arg: socket!);
             Assert.Throws<ArgumentException>(() => monitorEvent.ConvertArg<int>());
         }
-
-        [Fact]
-        public void INetMQMonitorCanBeMocked()
-        {
-            // This test demonstrates that INetMQMonitor can be mocked for testing
-            var mockMonitor = new MockNetMQMonitor();
-            
-            // Verify the mock implements the interface
-            INetMQMonitor monitor = mockMonitor;
-            
-            Assert.NotNull(monitor);
-            Assert.Equal("mock://endpoint", monitor.Endpoint);
-            Assert.False(monitor.IsRunning);
-            
-            // Verify we can subscribe to events
-            var eventReceived = false;
-            monitor.EventReceived += (s, e) => { eventReceived = true; };
-            
-            // Trigger the event
-            mockMonitor.RaiseEventReceived();
-            
-            Assert.True(eventReceived);
-        }
-
-        // Simple mock implementation to demonstrate INetMQMonitor is mockable
-        private class MockNetMQMonitor : INetMQMonitor
-        {
-            public string Endpoint => "mock://endpoint";
-            public bool IsRunning { get; private set; }
-            public TimeSpan Timeout { get; set; }
-
-            public event EventHandler<NetMQMonitorEventArgs>? EventReceived;
-#pragma warning disable CS0067 // Event is never used - these are part of the interface contract
-            public event EventHandler<NetMQMonitorSocketEventArgs>? Connected;
-            public event EventHandler<NetMQMonitorErrorEventArgs>? ConnectDelayed;
-            public event EventHandler<NetMQMonitorIntervalEventArgs>? ConnectRetried;
-            public event EventHandler<NetMQMonitorSocketEventArgs>? Listening;
-            public event EventHandler<NetMQMonitorErrorEventArgs>? BindFailed;
-            public event EventHandler<NetMQMonitorSocketEventArgs>? Accepted;
-            public event EventHandler<NetMQMonitorErrorEventArgs>? AcceptFailed;
-            public event EventHandler<NetMQMonitorSocketEventArgs>? Closed;
-            public event EventHandler<NetMQMonitorErrorEventArgs>? CloseFailed;
-            public event EventHandler<NetMQMonitorSocketEventArgs>? Disconnected;
-#pragma warning restore CS0067
-
-            public void AttachToPoller<T>(T poller) where T : INetMQPoller
-            {
-                IsRunning = true;
-            }
-
-            public void DetachFromPoller()
-            {
-                IsRunning = false;
-            }
-
-            public void Start()
-            {
-                IsRunning = true;
-            }
-
-            public Task StartAsync()
-            {
-                IsRunning = true;
-                return Task.CompletedTask;
-            }
-
-            public void Stop()
-            {
-                IsRunning = false;
-            }
-
-            public void Dispose()
-            {
-                IsRunning = false;
-            }
-
-            public void RaiseEventReceived()
-            {
-                EventReceived?.Invoke(this, new NetMQMonitorSocketEventArgs(null!, "test", null!, SocketEvents.Connected));
-            }
-        }
     }
 }