Update tests and dll resolver (#336)

Raylib-cs.Tests/RaylibTests.cs

@@ -1,7 +1,18 @@
+using System.Runtime.CompilerServices;
 using Xunit;
 
 namespace Raylib_cs.Tests;
 
+using System.Collections.Generic;
+
+public static class BlittableHelper
+{
+    public static bool IsBlittable<T>()
+    {
+        return !RuntimeHelpers.IsReferenceOrContainsReferences<T>();
+    }
+}
+
 public class RaylibTests
 {
     private unsafe void CheckType<T>() where T : unmanaged