Add common intervals for `ValidatorService` and `LeanChainService`

[syjn99]

Describe the feature

#679 introduced redundant code block in ValidatorService and LeanChainService.

ream/crates/common/chain/lean/src/service.rs

Lines 51 to 75 in b699064

	// TODO: Duplicate clock logic from ValidatorService. May need to refactor later.
	// Get the Lean network specification.
	let network_spec = lean_network_spec();
	let seconds_per_slot = network_spec.seconds_per_slot;
	let genesis_time = network_spec.genesis_time;
	info!("LeanChainService started with genesis_time={genesis_time}");
	// Calculate the genesis instant from the genesis time (in seconds).
	let genesis_instant = UNIX_EPOCH + Duration::from_secs(genesis_time);
	// Assume genesis time is "always" in the future,
	// as we don't support syncing features yet.
	let interval_start = Instant::now()
	+ genesis_instant
	.duration_since(SystemTime::now())
	.expect("Genesis time is in the past");
	let mut tick_count = 0u64;
	let mut interval = interval_at(
	interval_start,
	Duration::from_secs(seconds_per_slot / INTERVALS_PER_SLOT),
	);
	interval.set_missed_tick_behavior(MissedTickBehavior::Burst);

ream/crates/common/validator/lean/src/service.rs

Lines 64 to 91 in b699064

	// TODO: Duplicate clock logic from LeanChainService. May need to refactor later.
	// Get the Lean network specification.
	let network_spec = lean_network_spec();
	let seconds_per_slot = network_spec.seconds_per_slot;
	let genesis_time = network_spec.genesis_time;
	info!(
	"ValidatorService started with {} validator(s), genesis_time={genesis_time}",
	self.keystores.len()
	);
	// Calculate the genesis instant from the genesis time (in seconds).
	let genesis_instant = UNIX_EPOCH + Duration::from_secs(genesis_time);
	// Assume genesis time is "always" in the future,
	// as we don't support syncing features yet.
	let interval_start = Instant::now()
	+ genesis_instant
	.duration_since(SystemTime::now())
	.expect("Genesis time is in the past");
	let mut tick_count = 0u64;
	let mut interval = interval_at(
	interval_start,
	Duration::from_secs(seconds_per_slot / INTERVALS_PER_SLOT),
	);
	interval.set_missed_tick_behavior(MissedTickBehavior::Burst);

As I wrote in the comment, it'll be great to have common way to "tick" by a global clock.

Additional context

Shariq's comment: #679 (comment)

[syjn99]

@shariqnaiyer Are you interested in this?

[shariqnaiyer]

@syjn99 Yes. Could I take this?