Dev tools reports surpringly low fps
The fps reported by the wasm4 dev tools seems surprising low - 30-45 fps for even the zig template cart, for example.

Firefox performance tools shows much closer to 60fps, and very little time taken in each frame loop.

Maybe there's a bug in the dev tools FPS measurement?

![image](https://user-images.githubusercontent.com/179146/149407205-a8f472f8-6f50-4d8f-b988-f381f15f3de0.png)
