Merge bitcoindevkit/bdk#2158: ci: check-docs for all workspace packages

Merge bitcoindevkit/bdk#2158: ci: check-docs for all workspace packages

9c8b564fb4d9fc0ecf6a03f1cd6668de73555eb3 fix(docs): in keychain_txout.rs and spk_client.rs (shinigami-777)
19d1269f814f445b0337d6c66cd694358afede18 ci: add new check-docs job, justfile recipe and documentation (shinigami-777)

Pull request description:

  fixes #2152

  ### Description

  This PR adds new CI job `check-docs` to validate that documentation builds for all workspace packages, also adds a new justfile recipe `just doc`.

  It also fixes the existing errors in `bdk_chain` and `bdk_core`.

  ### Changelog notice

  ```
  ### Added

  - ci: add new `check-docs` job.

  ### Changed

  - fix(docs): in `keychain_txout.rs` and `spk_client.rs`
  ```

  ### Checklists

  #### All Submissions:

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

  #### New Features:

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

  #### Bugfixes:

  * [ ] This pull request breaks the existing API
  * [ ] 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:
  oleonardolima:
    ACK 9c8b564fb4d9fc0ecf6a03f1cd6668de73555eb3

Tree-SHA512: ce072647410ba577f28317f1f64c28576517ad29115db09e8231cb756a0e70dcbbe162592b7ab2cad73a67b0db8f727d48dc775817c2530d9f3c83f75832d859