fix: Fixes issue with wepoll losing GCHandle. (#1039)

- [X] Fixes issue with wepoll losing GCHandle.
- [X] `NetState.Disconnect()` is no longer thread safe.
  - Use `Core.LoopContext.Post()` to post disconnects
- [X] Optimizes PollGroup by not processing IntPtr -> GCHandle for discard polls.

Projects/Server.Tests/Tests/Network/PollGroupTests.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Runtime.InteropServices;
+using System.Threading;
+using Server.Network;
+using Xunit;
+
+namespace Server.Tests.Network;
+
+public class PollGroupTests
+{
+    [Fact]
+    public void TestPollGroup()
+    {
+        // var group = new KQueuePollGroup();
+        var nss = new NetState[2048];
+        var handles = new IntPtr[2048];
+        for (var i = 0; i < nss.Length; i++)
+        {
+            nss[i] = PacketTestUtilities.CreateTestNetState();
+            handles[i] = (IntPtr)nss[i].Handle;
+        }
+
+        GC.AddMemoryPressure(10000000000);
+        GC.Collect();
+        GC.RemoveMemoryPressure(10000000000);
+        GC.Collect();
+
+        Thread.Sleep(1000);
+
+        for (var i = 0; i < nss.Length; i++)
+        {
+            Assert.Equal(nss[i].Handle, (GCHandle)handles[i]);
+        }
+
+        // group.Dispose();
+    }
+}