Merge bitcoindevkit/bdk#1397: Introduce proptesting, starting with `CheckPoint::range`

446b045161ebad3fbdf0ea96e8ff6f9da8ad212c test(chain): introduce proptest for `CheckPoint::range` (志宇)

Pull request description:

  ### Description

  This is based on #1369. It made sense for me to introduce the `CheckPoint::range` test as a proptest. I think we should also start introducing it for other methods too.

  ### Changelog notice

  * Added proptest for `CheckPoint::range`.

  ### 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

Top commit has no ACKs.

Tree-SHA512: 2d8aad5a1ad152413fbc716fed4a47ad621e723928c5331728da2fbade995ebd677acfa05d2e7639d74d0f66e0971c72582d9cd562ea008b012774057b480d62