some cleanup

SDL3/ImGuiUserData.cs

@@ -0,0 +1,35 @@
+using System.Runtime.InteropServices;
+
+namespace SDL3_TestingSuite.SDL3;
+
+public unsafe static class ImGuiUserData<T> where T : class
+{
+    public static void* Store(T value)
+    {
+        if (value == null)
+            return null;
+
+        GCHandle handle = GCHandle.Alloc(value, GCHandleType.Normal);
+        return (void*)GCHandle.ToIntPtr(handle);
+    }
+
+    public static T? Get(void* ptr)
+    {
+        if (ptr == null)
+            return null;
+
+        GCHandle handle = GCHandle.FromIntPtr((nint)ptr);
+        return (T?)handle.Target;
+    }
+
+    public static void Free(void* ptr)
+    {
+        if (ptr == null)
+            return;
+
+        GCHandle handle = GCHandle.FromIntPtr((nint)ptr);
+
+        if (handle.IsAllocated)
+            handle.Free();
+    }
+}