Investigate and match Scratch's timer implementation

[towerofnix]

The current timer implementation in Leopard is very rudimentary:

https://github.com/leopard-js/leopard/blob/25652b187ab1f5876844316a8e7ba492e4891319/src/Project.js#L251-L254

This would be quite dandy if that's how the timer worked in Scratch, too, but it's not 📦

See this project I made last year which shows that the timer block is only updated once every rendered Scratch frame. (The main project loop runs many times in one frame unless you click "simulate movement", which enables requesting a screen redraw every tick.)

See all the gruesome details in scratch-vm: clock.js, sequencer.js.

[another-m00]

Related Timer implementation is Scratch-vm

[another-m00]

It appears that the timer itself was implemented pretty similarly, except they used this date method as fallback for the performance counter