Gloas fork choice implementation

[michaelsproul]

Description

This is an issue to track implementation of the fork choice changes for Gloas.

In particular, this is a place to note down ideas and requirements for fork choice, while implementing/reviewing lower layers of the Gloas spec. We can also sketch out approaches to the fork choice implementation here.

[michaelsproul]

In Gloas envelope processing, we are using the DB to read the execution payload bid for the envelope's beacon block. It would be possible to use fork choice for this if the bid were added to ProtoBlock. This is a relatively small optimisation, as reading a block from the DB should be quick.

lighthouse/beacon_node/beacon_chain/src/envelope_verification.rs

Lines 236 to 238 in 2985ede

	// TODO(EIP-7732): this should probably be obtained from the ProtoBlock instead of the DB
	// but this means the ProtoBlock needs to include something like the ExecutionBid
	// will need to answer this question later.

I don't think we need to action this right now.

[michaelsproul]

As an optimisation we could save the Fork from the state for blocks, and use this to signature-verify envelopes. This was never done previously because a block could have a different fork from its parent, or there could be numerous skipped slots. But for envelopes it's a nice optimisation, because block+envelope are from the same slot and must have the same Fork.