Get attester duties.

Requests the beacon node to provide a set of attestation duties, which should be performed by validators, for a particular epoch.

Duties should only need to be checked once per epoch, however a chain reorganization (of > MIN_SEED_LOOKAHEAD epochs) could occur, resulting in a change of duties. For full safety, you should monitor head events and confirm the dependent root in this response matches:

• event.previous_duty_dependent_root when compute_epoch_at_slot(event.slot) == epoch

• event.current_duty_dependent_root when compute_epoch_at_slot(event.slot) + 1 == epoch

• event.block otherwise

The dependent_root value is get_block_root_at_slot(state, compute_start_slot_at_epoch(epoch - 1) - 1) or the genesis block root in the case of underflow.