[Roshambo] Sync stims with screen refresh rate

[mesca]

The current code does not make use of the scheduler.asap() method, which synchronizes events with screen refreshes. For an example on how to use this feature, see the oddball demo:

demos/oddball/oddball/www/assets/js/app.js

Line 184 in 2c682f8

await this.scheduler.asap(() => {