Merge #1988: Detect new mempool txs

51ee99a docs(bitcoind_rpc): fixed typo in docs (Wei Chen)
73ab1eb chore(bitcoind_rpc): Make clippy happy (志宇)
7e894f4 feat(bitcoind_rpc)!: Use `getrawmempool` without verbose (志宇)
05464ec fix(bitcoind_rpc)!: Simplify emitter (志宇)
67dfb0b test(bitcoind_rpc): Detect new mempool txs (志宇)

Pull request description:

  ### Description

  There is a bug in `bdk_bitcoind_rpc` where some new mempool transactions will not be emitted at all.

  This problem exists because the avoid-re-emission logic depends on rounded-to-nearest-second timestamps.

  The fix is to just emit all mempool transactions but wrap them in `Arc`s so that emission becomes cheap.

  **Background:** I tried using `bdk_bitcoind_rpc` as the chain-source to write an example to showcase the [`IntentTracker`](bitcoindevkit/bdk_wallet#257). However, `bdk_bitcoind_rpc` failed to emit some mempool transactions.

  ### Notes to the reviewers

  The test added in c22c68f fails without these fixes.

  Some tests are removed as they are no longer relevant.

  ### Changelog notice

  ```md
  Fixed:
  - Some mempool transactions not being emitted at all. The fix is to replace the avoid-re-emission-logic with one which emits all mempool transactions.
  ```

  ### 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

  #### Bugfixes:

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

ACKs for top commit:
  nymius:
    cACK 51ee99a
  LagginTimes:
    Re-ACK 51ee99a

Tree-SHA512: 04e180e1d28c3f4c581a61ccac95e8e7e6927123d272ed07eae0ae51bf70799df44298b47ba0e49a309fd76366875e8d18d73478252931713137844857b8ed5a

Author: evanlinjin