Separate type for aggregated committee attestation

[ensi321]

Description

Introducing separate container for aggregated attestation in a committee. The new container replaces the unnecessary committee bits with committee index. It also has 63x shorter max length than Attestation on aggregation_bits which yields max size going from 16.23kb to 0.48kb. This ensures aggregates with 63 committees worth of zeros in aggregation bits with not be deserialized.

The current Attestation represents aggregated attestation both on-chain and in a committee. Having a dedicated container for committee attestation improves readability and removes the need to maintain a one-bit-set committee bit list.

[ppopth]

Referencing https://github.com/ethereum/consensus-specs/pull/3900#issuecomment-2383952335 and https://github.com/ethereum/consensus-specs/pull/3787 which have kind of similar ideas.

[leolara]

Please, fix that one of the checks is failing