Merge bitcoindevkit/bdk#2056: fix(core) `Checkpoint::drop` memory leak

0bd93dad114b90c3f08df9cc892625e250edb718 fix(core): Memory leak bugs in `CheckPoint::drop` impl (志宇)

Pull request description:

  based on #1997, depends on #2055

  ### Description

  Fix memory leak bug in CheckPoint::drop by using Arc::into_inner.

  Add tests (from the old PR) for memory leak + stack overflow when dropping CheckPoint.

  ### Notes to the reviewers

  It should be merged after #2055.

  ### Changelog notice

  ```
  ### Fix:
  - Fix memory leak bug in CheckPoint::drop by using `Arc::into_inner`.
  ```

  ### Checklists

  #### All Submissions:

  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)

  #### 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:
  evanlinjin:
    ACK 0bd93dad114b90c3f08df9cc892625e250edb718

Tree-SHA512: f61bd7ee19a6eb4e0f0275882d8c7b9f0e050e868e1e7a51b4089c8c71d14478905d900c619bebe71e4ffe7117400d99e4604d6a16e3b9a7515755d3f3250c90