API renames, change ref renderer to in renderer in IDrawable, make Layer implement IDrawable.

TestGame/Circle2d.cs

@@ -0,0 +1,13 @@
+using DaggerFramework.Rendering;
+using System.Drawing;
+
+
+namespace DaggerFramework;
+
+public class Circle2d : Drawable2d
+{
+    public override void OnDraw(in Renderer renderer)
+    {
+        renderer.DrawCircle(32f, Color.AliceBlue);
+    }
+}