tick (delay = 0) {
    fastNow += delay - RESOLUTION_MS + 1
    onTick()
    onTick()
  }
Trigger the onTick function to process the fastTimers array.
Exported for testing purposes only.
Marking as deprecated to discourage any use outside of testing.
@deprecated
@param {number} [delay=0] The delay in milliseconds to add to the now value.