EIP-8025: Proof before payload

[kevaundray]

Open question:

Can we assume that the payload will arrive before the proof?

Some things to consider are:

• a node being reorged; in that case they maye receive a proof for a fork before they receive the block
• Probably want to copy what blobs do

[kevaundray]

Tau has pointed to the specs doing what blobs do here: https://github.com/ethereum/consensus-specs/blob/master/specs/_features/eip8025/p2p-interface.md#execution_proof