feat(vm): IHost.Sleep seam + dispatch 0xc8 (headless hosts no-op; parity held)

- IHost.Sleep(long duration); VM case "sleep" forwards the raw operand.
- 8 non-Godot hosts no-op Sleep; RecordingHost records it.
- SleepDispatchTests (51 green); sweep unchanged 284 exit / 13 STEP-LIMIT.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

engine/Age.Engine.Tests/CallScriptTests.cs

@@ -15,6 +15,7 @@ public class CallScriptTests
     {
         public void ShowText(int o, string t) { }
         public void WaitForInput() { }
+        public void Sleep(long duration) { }
         public void CreateTexture(int s, int w, int h) { }
         public void SetTexture(long r, int s) { }
         public void DrawTexture(int s, int sx, int sy, int w, int h, int dx, int dy) { }