### Describe the feature ### This issue should Implement the new functions introduced and listed below and modify the existing functions listed below - Implements compute_proposer_indices(): https://ethereum.github.io/consensus-specs/specs/fulu/beacon-chain/#new-compute_proposer_indices - Modifies get_beacon_proposer_index(): https://ethereum.github.io/consensus-specs/specs/fulu/beacon-chain/#modified-get_beacon_proposer_index - Implements get_beacon_proposer_indices(): https://ethereum.github.io/consensus-specs/specs/fulu/beacon-chain/#new-get_beacon_proposer_indices - Modifies process_epoch(): https://ethereum.github.io/consensus-specs/specs/fulu/beacon-chain/#modified-process_epoch - Implements process_proposer_lookahead(): https://ethereum.github.io/consensus-specs/specs/fulu/beacon-chain/#new-process_proposer_lookahead - Modifies BeaconState: https://github.com/ethereum/consensus-specs/blob/master/specs/fulu/beacon-chain.md#beaconstate