Merge bitcoindevkit/bdk#1857: feat(rpc)!: Update `Emitter::mempool` to support `evict...

8513d83a2ef2fe748e9007984187a7f08d256ee6 feat(bitcoind_rpc)!: Reduce friction of `Emitter` API. (志宇)
0a02d26835a41556cf0f6899f97fdb42bf4d0f9d feat(chain): Add convenience conversions for `CanonicalTx` (志宇)
d11f6efe8f6feddaa115cde32ebead19f92c2f64 feat(graph): add convenience function for inserting relevant `evicted_at`s (Wei Chen)
28ef7c9a22c4364925329628fa84fd09ecc82e2e refactor(rpc)!: update `mempool` interface and test code (valued mammal)

Pull request description:

  Fixes #1740

  ### Description

  Work for this began as part of #1811, based on this [comment](https://github.com/bitcoindevkit/bdk/pull/1811#discussion_r1945941691).

  `Emitter::mempool` now returns a `MempoolEvent` which provides the data for tracking `evicted_at`:

  ```
  pub struct MempoolEvent {
      /// Unemitted transactions or transactions with ancestors that are unseen by the receiver.
      ///
      /// To understand the second condition, consider a receiver which filters transactions based on
      /// whether it alters the UTXO set of tracked script pubkeys. If an emitted mempool transaction
      /// spends a tracked UTXO which is confirmed at height `h`, but the receiver has only seen up to
      /// block of height `h-1`, we want to re-emit this transaction until the receiver has seen the
      /// block at height `h`.
      pub new_txs: Vec<(Transaction, u64)>,

      /// [`Txid`]s of all transactions that have been evicted from mempool.
      pub evicted_txids: HashSet<Txid>,

      /// The latest timestamp of when a transaction entered the mempool.
      ///
      /// This is useful for setting the timestamp for evicted transactions.
      pub latest_update_time: u64,
  }
  ```

  ### Changelog notice

  * Change `Emitter::mempool` to return `MempoolEvent`s which contain mempool-eviction data.
  * Change `Emitter::client` to have more relaxed generic bounds. `C: Deref, C::Target: RpcApi` are the new bounds.
  * Add conversion impls for `CanonicalTx` to `Txid`/`Arc<Transaction>`.
  * Add `ChainPosition::is_unconfirmed` method.

  ### 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 fmt` and `cargo clippy` before committing

  #### New Features:

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

  #### Bugfixes:

  * [x] This pull request breaks the existing API
  * [x] I've added tests to reproduce the issue which are now passing
  * [x] I'm linking the issue being fixed by this PR

ACKs for top commit:
  ValuedMammal:
    ACK 8513d83a2ef2fe748e9007984187a7f08d256ee6

Tree-SHA512: 28149458085dc4cefefe06656769d701b53f891c1ecb5d400aba8b23d63c026d6e4db1c9e6f47c8ad167edc1559d897d28e9bb71e7bd144792b5cecc0bcd31ce