Merge bitcoin/bitcoin#34873: net: fix premature stale flagging of unpicked private broadcast txs

325afe664d net: delay stale evaluation and expose time_added in private broadcast (Mccalabrese)
999d18ab1c net: introduce TxSendStatus internal state container (Mccalabrese)

Pull request description:

  **Motivation**
  Currently, freshly added transactions in `private_broadcast` are almost immediately flagged and logged as stale by the `resend-stale` job.

  **The Bug**
  `m_transactions` maps a transaction to a `std::vector<SendStatus>`. When `try_emplace` adds a new transaction, this vector is empty. When `GetStale()` runs, `DerivePriority()` evaluates the empty vector and returns a default `Priority` struct where `last_confirmed` evaluates to the Unix Epoch (Jan 1, 1970). The stale checker sees a 50-year-old timestamp and flags it on the next resend-stale cycle.

  **The Fix**
  Rather than modifying the transient `Priority` struct or creating a "Zombie Transaction" edge case by ignoring transactions with 0 picks, this PR modifies the state container:
  * Wraps the `SendStatus` vector in a new `TxSendStatus` struct inside `private_broadcast.h`.
  * `TxSendStatus` automatically captures `time_added` upon emplace.
  * `GetStale()` now checks `p.num_confirmed == 0` to measure age against `time_added` using a new 5-minute `INITIAL_STALE_DURATION` grace period, falling back to `last_confirmed` and the standard 1-minute `STALE_DURATION` once network interaction begins.

  **Additional Polish**
  * Exposed `time_added` via the `getprivatebroadcastinfo`  RPC endpoint so users can see when a transaction entered the queue.
  * Added a dedicated `stale_unpicked_tx` test case and updated `private_broadcast_tests.cpp` to properly mock the passage of time for the new grace period.
  Closes #34862

ACKs for top commit:
  achow101:
    ACK 325afe664d
  andrewtoth:
    ACK 325afe664d
  vasild:
    ACK 325afe664d

Tree-SHA512: b7790aa5468f7c161ed93e99e9a6d8b4db39ff7d6d6a920764afd18825e08d83bc30b3fb0debeb6175730b5d2496c6be67f3be8674be93f4d07b1e77d17b4a14

src/net_processing.cpp

@@ -1866,7 +1866,8 @@ std::vector<CTransactionRef> PeerManagerImpl::AbortPrivateBroadcast(const uint25
     std::vector<CTransactionRef> removed_txs;
 
     size_t connections_cancelled{0};
-    for (const auto& [tx, _] : snapshot) {
+    for (const auto& tx_info : snapshot) {
+        const CTransactionRef& tx{tx_info.tx};
         if (tx->GetHash().ToUint256() != id && tx->GetWitnessHash().ToUint256() != id) continue;
         if (const auto peer_acks{m_tx_for_private_broadcast.Remove(tx)}) {
             removed_txs.push_back(tx);