Make `w4 watch` less resource-hungry
It looks like `w4 watch` busy-looping waiting to re-build files if they are changed. I wonder if it is possible to avoid busy-looping and what would be the thing that makes it do so. I looked at the code and don't seem to understand where it could be without further testing.

![image](https://github.com/aduros/wasm4/assets/20167110/1fd2be0e-7224-4e0c-9d0f-8cecadf60498)
