Gloas vc ptc duty

[shane-moore]

Changes

• added polling of ptc duties to the VC per spec

How This Works

• The VC is currently checking whether one of its registered validators are in a voting committee, such as sync or attestation, or if they are the proposer for a slot. With epbs, it's possible for a validator to also be in a ptc committee for at most one slot of the epoch. More context on how validators are selected to be in a ptc was discussed on discord.

Implemented in the PR

duties_service will now spawn a background polling task for the current and next epoch to check whether any of the registered validators are in a ptc committee. Since re-org is possible, we also poll every slot. The beacon node querying is performed by new request endpoint POST validator/duties/ptc/{epoch} per beacon api spec.

To save on bandwidth similar to attestation committee polling, the ptc polling will make a tiny initial requests to learn the dependent_root, compare with the cached dependent_root, and only fetch full duties for the epoch if the root has changed (or if the root is unknown like for a new epoch). Old duties are pruned based on HISTORICAL_DUTIES_EPOCHS.

Todo

• add tests noted in the diffs
• create beacon node (server side) response that will send the ptc duties to the VC. Some of this work has already been done in other PR's such as the get_ptc helper, but the warp implementation still needs to be complete as to send the response to the VC

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