Reserve space for one validator sweep withdrawal

[jtraglia]

In order for update_next_withdrawal_validator_index to function properly, the last withdrawal must be from the validator sweep (or empty).

consensus-specs/specs/capella/beacon-chain.md

Lines 466 to 480 in ea1b812

	def update_next_withdrawal_validator_index(
	state: BeaconState, withdrawals: Sequence[Withdrawal]
	) -> None:
	# Update the next validator index to start the next withdrawal sweep
	if len(withdrawals) == MAX_WITHDRAWALS_PER_PAYLOAD:
	# Next sweep starts after the latest withdrawal's validator index
	next_validator_index = ValidatorIndex(
	(withdrawals[-1].validator_index + 1) % len(state.validators)
	)
	state.next_withdrawal_validator_index = next_validator_index
	else:
	# Advance sweep by the max length of the sweep if there was not a full set of withdrawals
	next_index = state.next_withdrawal_validator_index + MAX_VALIDATORS_PER_WITHDRAWALS_SWEEP
	next_validator_index = ValidatorIndex(next_index % len(state.validators))
	state.next_withdrawal_validator_index = next_validator_index

[jihoonsong]

While either adding the assertion or switching has_reached_limit from == to >= achieves the same goal, I'd prefer the prior as it makes it explicit what the precondition of each withdrawal function is. With those assertions, len(all_withdrawals) cannot be greater than withdrawals_limit, but I don't think it hurts to change to >=.

[jtraglia]

While either adding the assertion or switching has_reached_limit from == to >= achieves the same goal, I'd prefer the prior as it makes it explicit what the precondition of each withdrawal function is. With those assertions, len(all_withdrawals) cannot be greater than withdrawals_limit, but I don't think it hurts to change to >=.

I agree with this & this is the reason why I did both (asserts & comp changes).

[potuz]

LGTM

[jihoonsong]

Given that we have four withdrawal functions, passing max_withdrawals_limit or something similar would make these functions less stateful. Nonetheless, this PR achieves what it aims for.