Show the timestamp of the transaction in tx-pool through rpc

[quake]

#3894 added a timestamp to record the transaction when it entering the tx-pool, suggest to display this field in theget_transaction rpc, it's helpful to debug or re-send a long pending tx by checking this timestamp.

[eval-exec]

The current TxStatus definition is this:

ckb/util/types/src/core/tx_pool.rs

Lines 102 to 116 in 98678a8

	#[derive(Clone, Debug, PartialEq, Eq)]
	pub enum TxStatus {
	/// Status "pending". The transaction is in the pool, and not proposed yet.
	Pending,
	/// Status "proposed". The transaction is in the pool and has been proposed.
	Proposed,
	/// Status "committed". The transaction has been committed to the canonical chain.
	Committed(H256),
	/// Status "unknown". The node has not seen the transaction,
	/// or it should be rejected but was cleared due to storage limitations.
	Unknown,
	/// Status "rejected". The transaction has been recently removed from the pool.
	/// Due to storage limitations, the node can only hold the most recently removed transactions.
	Rejected(String),
	}

I think we can change TxStatus to this:
change Pending to Pending(u64), change Proposed to Proposed(u64).
(just add a inner u64 value in Pending and Proposed to represent the timestamp when the tx was enter the tx-pool.)

/// Tx-pool transaction status
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum TxStatus {
    /// Status "pending". The transaction is in the pool, and not proposed yet.
    Pending(u64),  // inner value is the timestamp when the tx enter the pool

    /// Status "proposed". The transaction is in the pool and has been proposed.
    Proposed(u64), // inner value is the timestamp when the tx enter the pool

    /// Status "committed". The transaction has been committed to the canonical chain.
    Committed(H256),
    /// Status "unknown". The node has not seen the transaction,
    /// or it should be rejected but was cleared due to storage limitations.
    Unknown,
    /// Status "rejected". The transaction has been recently removed from the pool.
    /// Due to storage limitations, the node can only hold the most recently removed transactions.
    Rejected(String),
}

Cc. @zhangsoledad

[doitian]

I would suggest adding an RPC like Bitcoin getmempoolentry.

[eval-exec]

I would suggest adding an RPC like Bitcoin getmempoolentry.

Agree, I would like to work on this.

[zhangsoledad]

@eval-exec

I recommend adding a field

#[derive(Clone, Debug)]
pub struct TransactionWithStatus {
    /// The transaction.
    ......
    pub cycles: Option<core::Cycle>.
    pub timestamp: Option<u64>.
}

Instead of modifying the structure of TxStatus

For json parser,
adding a filed is much more friendly than modifying the object's structure.