[Feature]: Curp Refactoring about xline HOT 6 CLOSED

/// Relevant context for Curp
struct Context<C: Command> {
    /// Id of the server
    id: ServerId,
    /// Other server ids and addresses
    others: HashSet<ServerId>,
    /// Timeout
    timeout: Arc<ServerTimeout>,
    /// Cmd board for tracking the cmd sync results
    cb: CmdBoardRef<C>,
    /// Speculative pool
    sp: SpecPoolRef<C>,
    /// Tx to send leader changes
    leader_tx: broadcast::Sender<Option<ServerId>>,
    /// Election tick
    election_tick: AtomicU8,
    /// Heartbeat opt out flag
    hb_opt: AtomicBool,
    /// Tx to send cmds to execute and do after sync
    cmd_tx: Box<dyn CmdExeSenderInterface<C>>,
}

pub(super) struct State {
    /* persisted state */
    /// Current term
    pub(super) term: u64,
    /// Candidate id that received vote in current term
    pub(super) voted_for: Option<ServerId>,

    /* volatile state */
    /// Role of the server
    pub(super) role: Role,
    /// Cached id of the leader.
    pub(super) leader_id: Option<ServerId>,
}

pub(super) struct CandidateState<C> {
    /// Collected speculative pools, used for recovery
    pub(super) sps: HashMap<ServerId, Vec<Arc<C>>>,
    /// Votes received in the election
    pub(super) votes_received: u64,
}

pub(super) struct LeaderState {
    /// For each server, index of the next log entry to send to that server
    pub(super) next_index: HashMap<ServerId, usize>,
    /// For each server, index of highest log entry known to be replicated on server
    pub(super) match_index: HashMap<ServerId, usize>,
}

pub(super) struct Log<C: Command> {
    /// Log entries
    pub(super) entries: Vec<LogEntry<C>>,
    /// Index of highest log entry known to be committed
    pub(super) commit_index: usize,
    /// Index of highest log entry applied to state machine
    pub(super) last_applied: usize,
}