Clock and timers

Nanosecond time, a test clock and a live clock.

Test clock

The source of determinism for timers. Advancing it returns every timer and alert in the window, ordered by fire time and then by registration order, so two runs on the same input fire identically.

Timer firing

The engine steps the clock one firing time at a time, so a timer set inside on_timer is scheduled from its firing time.

Live clock

Reads real time. A live runner passes it to the engine through idle.