Consider adding a lookahead access function to remove duplicate code

[dantaik]

function _lookaheadEntry(uint256 index) internal view returns (LookaheadBufferEntry storage) {
    return lookahead[index % LOOKAHEAD_BUFFER_SIZE];
}

introducing the above function will make a lot of duplicate % LOOKAHEAD_BUFFER_SIZE go away from PreconfTaskManager.sol to simply the code.

[AnshuJalan]

Added in: NethermindEth/Taiko-Preconf-AVS#180