EIP-4895: Beacon chain push withdrawals as operations

[anvacaru]

Implementing withdrawal operations as specified in EIP-4895.

• adding a new <withdrawals> cell map subconfiguration to the <network> that is used to keep track of withdrawals.
  Similar to how <messages> is implemented, <withdrawals> has two additional Lists:
  • <withdrawalsPending> to keep track of the withdrawals that need to be applied.
  • <withdrawalsOrder> to preserve the order of the withdrawals during the check rules after the execution has finished.
• adding new EthereumCommands productions:
  • load "withdraw" that handles the rlp decoding of the withdrawals array. For each item, the following two productions will be applied:
  • mkWD - that creates a new <withdrawal> cell map item.
  • loadWithdraw - that initialises the newly created <withdrawal> with values that are provided from the rlp payload.
  • newWithdrawalID - function that is used to generate a new index**.
• updating .k specs

** newWithdrawalID shouldn't be necesary, as according to the specs:

Withdrawals provide key information from the consensus layer:
1. a monotonically increasing index, starting from 0, as a uint64 value that increments by 1 per withdrawal to uniquely identify each withdrawal
4. a nonzero amount of ether given in Gwei (1e9 wei) as a uint64 value.

So the provided withdrawal index should be enough to keep track of the withdrawals.
However, the conformance tests have multiple withdrawals with the 0 index and 0 amount (example).

[anvacaru]

These two remain skipped as the 0x0a precompiled contract has not yet been added.

[dwightguth]

I didn't review the whole PR in detail, but it largely looks fine and I did review the changes to block finalization in detail and they look correct.

You might consider using some kind of named constant to represent the conversion factor from GWEI to WEI though. It's not critical, but something to consider for readability.