VC time updates

[paulhauner]

Description

The DutiesService (and others) in the VC presently doing their polling by waiting until the beginning of a slot then starting a repeating 12s timer:

lighthouse/validator_client/src/duties_service.rs

Lines 471 to 478 in 65dcdc3

	let mut interval = {
	let slot_duration = Duration::from_millis(spec.milliseconds_per_slot);
	// Note: `interval_at` panics if `slot_duration` is 0
	interval_at(
	Instant::now() + duration_to_next_slot + TIME_DELAY_FROM_SLOT,
	slot_duration,
	)
	};

This generally works well, however it doesn't account for the scenario where the time is incorrect and changes during operation. E.g., if your VC is 5s slow when it starts, even if you change your clock the DutiesService will keep using that old time.

Steps to Resolve

Options:

• Change to a mechanism that adjusts with the system clock.
• Check against the slot clock when the services start and log an error if their out of sync (not ideal, but interesting stop-gap for the time being).