refactor: easings have a singleton base so we don't create an unnecessary instance or cache everytime

Engine.Systems/Tween/Tween.cs

@@ -43,7 +43,7 @@ internal class Tween : ITween
     public float Progress { get; internal set; } = 0f;
     private float _counter = 0f;
 
-    public IEasing Easing { get; set; } = new EaseLinear();
+    public IEasing Easing { get; set; } = EaseLinear.Instance;
     public float Value => Easing.Evaluate(Progress);
 
     public float Counter