Allow alternative methods of proposer payments in validation api.

[dvush]

📝 Summary

This will allow validation API to accept blocks where:

• proposer payment is plain transfer to the fee recipient
• proposer payment is internal payment to the fee recipient made through the smart contract
• fee recipient is set to coinbase and accepts payment directly

The way we calculate profit is:

• check balance difference of the fee recipient after each tx in the block
• if its positive we count it toward total block profit
• if its negative we ignore it, but if fee recipient is also a coinbase we add tip payed by the tx to profit
• when profit is calculated we make sure that claimed profit is equal or bigger than calculated profit

Some features of this method:

• withdrawals from the fee recipient don't decrease profit of the bid
• deposits to the fee recipient address can be claimed as a profit
• builders that ignore withdrawals/deposits of the fee recipients and just calculate balance diff of it before and after block will work.

---

• I have seen and agree to CONTRIBUTING.md

[metachris]

would love a review from @Ruteri too

[Ruteri]

Should the default behaviour be to enforce the direct transfer?
That would make the new change opt-in which I think is going to be nicer.

[Ruteri]

Hm, maybe == 0 would help us notice bugs faster

[dvush]

= here is so that builders can underestimate their profits. e.g. if you don't count payments to the proposals and withdrawals correctly.

[dvush]

closed in favor of #93