Thanks for the report. This was a tricky one when I was setting up the chapter; I wanted to include timing, as a teaching vehicle for tackling that side of things. I also wanted to keep it simple - avoid overloading the reader too much with the introductory game.
You can greatly reduce the amount of CPU usage by adding .with_fps_cap(30.0) to the builder call in main(). That adds CPU sleep time in between frames.
I’ll do a bit of testing/playing around and see what the impact would be on the book as a whole to include this in by default.