Emit clock slot event on updated currentSlot

[wemeetagain]

Motivation

Currently, we can run into a situation where the clock.currentSlot is updated but that slot's event has not yet been triggered (and important callbacks have not yet been executed).
This can lead to confusing bugs, like:

Eph 1/3 0.084 [NODE-A CHAIN]    error: Block error slot=11 code=BLOCK_ERROR_BEACON_CHAIN_ERROR, error={"code":"FORKCHOICE_ERROR_INVALID_BLOCK","err":{"code":"FUTURE_SLOT","currentSlot":10,"blockSlot":11}}
Error: FORKCHOICE_ERROR_INVALID_BLOCK
    at LodestarForkChoice.onBlock (/home/runner/work/lodestar/lodestar/packages/fork-choice/src/forkChoice/forkChoice.ts:238:13)
    at Object.runStateTransition (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/stateTransition.ts:151:14)
    at Object.processBlock (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/process.ts:60:11)
    at processBlockJob (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/processor.ts:80:5)
    at Object.job (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/processor.ts:59:42)
    at Object.wrapError (/home/runner/work/lodestar/lodestar/packages/lodestar/src/util/wrapError.ts:18:32)
    at Timeout.JobQueue.runJob [as _onTimeout] (/home/runner/work/lodestar/lodestar/packages/lodestar/src/util/queue/index.ts:93:17)
Error: BLOCK_ERROR_BEACON_CHAIN_ERROR
    at Object.processBlock (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/process.ts:73:11)

Where even though the block passes validation (including that block.slot >= clock.currentSlot), the fork choice store isn't yet updated.

Description

Update the clock.currentSlot getter to trigger clock events if the call results in an updated slot. This will give important slot event handlers a chance to run before the consumer of a currentSlot continues.

Specifically, with regards to the above error, when the block in question is now validated (and checked against clock.currentSlot), the slot event handler will be called, allowing the fork choice to be updated before continuing block processing at that slot.

[codeclimate]

Code Climate has analyzed commit 143e4c3 and detected 0 issues on this pull request.

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[dapplion]

This may be necessary to potentially fix a bug in #2416 where the fork-choice currentSlot is not in sync with the rest of the beacon node

Eph 1/3 0.084 [NODE-A CHAIN]    error: Block error slot=11 code=BLOCK_ERROR_BEACON_CHAIN_ERROR, error={"code":"FORKCHOICE_ERROR_INVALID_BLOCK","err":{"code":"FUTURE_SLOT","currentSlot":10,"blockSlot":11}}
Error: FORKCHOICE_ERROR_INVALID_BLOCK
    at LodestarForkChoice.onBlock (/home/runner/work/lodestar/lodestar/packages/fork-choice/src/forkChoice/forkChoice.ts:238:13)
    at Object.runStateTransition (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/stateTransition.ts:151:14)
    at Object.processBlock (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/process.ts:60:11)
    at processBlockJob (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/processor.ts:80:5)
    at Object.job (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/processor.ts:59:42)
    at Object.wrapError (/home/runner/work/lodestar/lodestar/packages/lodestar/src/util/wrapError.ts:18:32)
    at Timeout.JobQueue.runJob [as _onTimeout] (/home/runner/work/lodestar/lodestar/packages/lodestar/src/util/queue/index.ts:93:17)
Error: BLOCK_ERROR_BEACON_CHAIN_ERROR
    at Object.processBlock (/home/runner/work/lodestar/lodestar/packages/lodestar/src/chain/blocks/process.ts:73:11)

However, we should look in the future at how to do this cleanly. Potentially triggering expensive events on this getter sounds like an unpredictable bottleneck.

[twoeths]

there are build errors in CI

@chainsafe/lodestar: [1] src/chain/clock/LocalClock.ts:36:5 - error TS2322: Type 'number' is not assignable to type 'Timeout'.
@chainsafe/lodestar: [1] 
@chainsafe/lodestar: [1] 36     this.timeoutId = setTimeout(this.onNextSlot, this.msUntilNextSlot());