double getBlindedBlock timeout to 1 second

[tersec]

Only merge one of #4751 and this

This is from

nimbus-eth2/beacon_chain/validators/validator_duties.nim

Lines 691 to 717 in 17c0eee

	let blindedBlockParts = await getBlindedBlockParts[EPH](
	node, head, validator.pubkey, slot, randao, validator_index,
	node.graffitiBytes)
	if blindedBlockParts.isErr:
	# Not signed yet, fine to try to fall back on EL
	beacon_block_builder_missed_with_fallback.inc()
	return Opt.none BlockRef
	# These, together, get combined into the blinded block for signing and
	# proposal through the relay network.
	let (executionPayloadHeader, forkedBlck) = blindedBlockParts.get
	# This is only substantively asynchronous with a remote key signer
	let blindedBlock = awaitWithTimeout(
	getBlindedBeaconBlock[SBBB](
	node, slot, validator, validator_index, forkedBlck,
	executionPayloadHeader),
	500.milliseconds):
	Result[SBBB, string].err("getBlindedBlock timed out")
	if blindedBlock.isErr:
	info "proposeBlockMEV: getBlindedBeaconBlock failed",
	slot, head = shortLog(head), validator_index, blindedBlock,
	error = blindedBlock.error
	return Opt.none BlockRef
	# Before unblindAndRouteBlockMEV, can fall back to EL; after, cannot

But getBlindedBlock doesn't directly interact with MEV relays, and is only truly asynchronous at all if someone's using a remote keysigner. getBlindedBlockParts, rather, is the call which gets the header bid from the MEV relay.

The issue is that if the timeout hits after the slashing has been checked in

nimbus-eth2/beacon_chain/validators/validator_duties.nim

Lines 584 to 608 in 17c0eee

	proc getBlindedBeaconBlock[
	T: bellatrix_mev.SignedBlindedBeaconBlock |
	capella_mev.SignedBlindedBeaconBlock](
	node: BeaconNode, slot: Slot, validator: AttachedValidator,
	validator_index: ValidatorIndex, forkedBlock: ForkedBeaconBlock,
	executionPayloadHeader: bellatrix.ExecutionPayloadHeader |
	capella.ExecutionPayloadHeader):
	Future[Result[T, string]] {.async.} =
	withBlck(forkedBlock):
	when consensusFork >= ConsensusFork.Deneb:
	debugRaiseAssert $denebImplementationMissing & ": getBlindedBeaconBlock"
	return err("getBlindedBeaconBlock: Deneb blinded block creation not implemented")
	elif consensusFork >= ConsensusFork.Bellatrix:
	when not (
	(T is bellatrix_mev.SignedBlindedBeaconBlock and
	consensusFork == ConsensusFork.Bellatrix) or
	(T is capella_mev.SignedBlindedBeaconBlock and
	consensusFork == ConsensusFork.Capella)):
	return err("getBlindedBeaconBlock: mismatched block/payload types")
	else:
	return await blindedBlockCheckSlashingAndSign(
	node, slot, validator, validator_index,
	constructSignableBlindedBlock[T](blck, executionPayloadHeader))
	else:
	return err("getBlindedBeaconBlock: attempt to construct pre-Bellatrix blinded block")

it can effectively disable the local EL fallback, because the slashing protection already thinks it's produced a block.

500 milliseconds was somewhat arbitrary, and there hadn't been any timeout in non-remote keysigning setups, so reduce likelihood of this case.

[tersec]

#4751 is a better approach