Merge #1977: Add TxGraph::get_last_evicted

b555acb feat(chain): Add `TxGraph::get_last_evicted` (志宇)

Pull request description:

  ### Description

  Ideally, this would be included as a field in `TxNode`, however that would be a breaking change.

  ### Changelog notice

  ```md
  Added
  - `TxGraph::get_last_evicted`
  ```

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo +nightly fmt` and `cargo clippy` before committing

  #### New Features:

  ~* [ ] I've added tests for the new feature~
  * [x] I've added docs for the new feature

ACKs for top commit:
  evanlinjin:
    self-ACK b555acb

Tree-SHA512: f1661d204e89e400b93e17f51f890a591edcdeea95803c4c48b937b700f48d5f2d975fcf33def3c5e36df13809ac2cc75f99ffc99716fa38c356b253a61eb5cb

Author: evanlinjin

crates/chain/src/tx_graph.rs

@@ -410,6 +410,13 @@ impl<A> TxGraph<A> {
         })
     }
 
+    /// Get the `last_evicted` timestamp of the given `txid`.
+    ///
+    /// Ideally, this would be included in [`TxNode`], but that would be a breaking change.
+    pub fn get_last_evicted(&self, txid: Txid) -> Option<u64> {
+        self.last_evicted.get(&txid).copied()
+    }
+
     /// Calculates the fee of a given transaction. Returns [`Amount::ZERO`] if `tx` is a coinbase
     /// transaction. Returns `OK(_)` if we have all the [`TxOut`]s being spent by `tx` in the
     /// graph (either as the full transactions or individual txouts).