EIP-7549: attestation pool

[rkapka]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

This PR produces necessary changes to the attestation pool in order to extend it to Electra.

Currently attestations are keyed in the pool using [32]byte, which is an HTR of an Attestation/AttestationData or a result of calling hash.Proto on one of these two types. For all practical purposes, both HTR and hash.Proto are interchangeable. In fact, this PR abandons hash.Proto and uses HTR everywhere for uniformity.

We want to separate Phase0 and Electra attestations so that we don't mix them together in operations. An obvious solution is to key by version on top of the hash. We create an Id type and use it as the key in all attestation maps.

type Id struct {
	version int
	hash    [32]byte
}

This is sufficient for hashing full attestations, but not for attestation data (at least not without some additional work). In Electra committee index is stored in a new CommitteeBits field and the committee index of attestation data is always 0. This means that two Electra attestations with a different committee index but the same (slot, beacon block root, source, target) tuple will have equal attestation data. To fix this, we make a copy of Electra attestation data in the NewId constructor function, set its committee index to the value from CommitteeBits and hash that copy.

Other than changes to how we key attestations, this PR extends the pool with two new functions:

• AggregatedAttestationsBySlotIndexElectra
• UnaggregatedAttestationsBySlotIndexElectra