Update IL duty

[mehdi-aouadi]

New inclusion list committee assignment

A validator may be a member of the new Inclusion List Committee (ILC) for a given slot. To check for ILC assignments the validator uses the helper get_inclusion_committee_assignment(state, epoch, validator_index) where epoch <= next_epoch.

Inclusion list committee selection is only stable within the context of the current and next epoch.

def get_inclusion_committee_assignment(
        state: BeaconState,
        epoch: Epoch,
        validator_index: ValidatorIndex) -> Optional[Slot]:
    """
    Returns the slot during the requested epoch in which the validator with index ``validator_index``
    is a member of the ILC. Returns None if no assignment is found.
    """
    next_epoch = Epoch(get_current_epoch(state) + 1)
    assert epoch <= next_epoch

    start_slot = compute_start_slot_at_epoch(epoch)
    for slot in range(start_slot, start_slot + SLOTS_PER_EPOCH):
        if validator_index in get_inclusion_list_committee(state, Slot(slot)):
            return Slot(slot)
    return None