…ntation improvements

1103936 chore(style+docs): style and docs retouch (Leonardo Lima)
442789c chore(style): update new methods style (Leonardo Lima)
565d79e refactor(async): add common GET and POST methods (Leonardo Lima)
31dfa4b chore(docs): minor improvements on docstrings (Leonardo Lima)

Pull request description:

  <!-- You can erase any parts of this template not applicable to your Pull Request. -->

  ### Description

  It builds on top of #95. Applies minor improvements on some docstrings, and Cargo.toml standard.

  The main change is adding the common HTTP methods for the `AsyncClient`, it removes duplicated code from each Esplora API request, and follows the approach done for `BlockingClient`.

  It makes it easier to extract these methods into an `AsyncEsploraClient` trait (to be done in another PR, initially done here 9cbc387), which the user can implement with any HTTP client of its choice. Also, makes it simpler to rebase and update the `AsyncAnonymizedClient` from #67.

  <!-- Describe the purpose of this PR, what's being adding and/or fixed -->

  ### Notes to the reviewers

  It has some commits from #95, as it builds on top of it and should be merged afterward. Please let me know what you think about the proposed changes and approach.

  <!-- In this section you can include notes directed to the reviewers, like explaining why some parts
  of the PR were done in a specific way -->

  ### Changelog notice

  - Applies minor improvements on documentation.
  - Add common `get_response` and `post_request` methods to `AsyncClient`, previously duplicated through the esplora API calls. It follows the approach done for `BlockinClient`.

  <!-- Notice the release manager should include in the release tag message changelog -->
  <!-- See https://keepachangelog.com/en/1.0.0/ for examples -->

  ### 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

ACKs for top commit:
  ValuedMammal:
    ACK 1103936
  notmandatory:
    ACK 1103936

Tree-SHA512: 5579e0cba105f553782e419a16c26fc75b38a2ab8ee523f5ce5e2b9a4560503ef7f81faac546429851802efb66cf125cb36b49f20f088969a6ad580e644d43e5

…ome CI dependencies

1a4d5cf2c5271b722e115492557643dcab22df3f chore(rust+clippy): bump `edition` to 2021, and add `.clippy.toml` (Leonardo Lima)
b7636e8a5328d26c01249c79e03f33921760445b fix(fmt): apply suggested fixes from `rustfmt` (Leonardo Lima)
3f2ca2fdcb3c31a71a47082e9c9f67a126216be8 refactor(ci)!: add new `fmt` and `clippy` jobs (Leonardo Lima)
9f888c17b7f1ede4c9d752f64e96ba024a643167 chore(deps): bump `actions/checkout` from v3 to v4 (Leonardo Lima)

Pull request description:

  <!-- You can erase any parts of this template not applicable to your Pull Request. -->

  ### Description

  This PR does some improvements on CI, these are some changes that I ended up doing on other refactoring and feature PRs (making them too convoluted), but had a specific CI scope so I'm moving them to a specific PR.

  This PR does:

  - bump the `actions/checkout@v3` to `actions/checkout@v4`.
  - adds two new jobs for `fmt` and `clippy` (clippy has been moved to a specific job).
  - fix the newly found `fmt` problems.
  - bump the rust edition to `2021`.
  - adds `.clippy.toml` file with `msrv=1.63.0`.

  <!-- Describe the purpose of this PR, what's being adding and/or fixed -->

  ### Notes to the reviewers

  I hope this PR reduces the scope convolution from the other ones #67 #93, and makes the review easier.

  <!-- In this section you can include notes directed to the reviewers, like explaining why some parts
  of the PR were done in a specific way -->

  ### Changelog notice

  - Bump the `actions/checkout@v3` to `actions/checkout@v4`.
  - Adds two new jobs for `fmt` and `clippy` (clippy has been moved to a specific job).
  - Multiple fixes for the newly found `fmt` problems.
  - Bump the rust edition to `2021`.
  - Adds `.clippy.toml` file with `msrv=1.63.0`.

  <!-- Notice the release manager should include in the release tag message changelog -->
  <!-- See https://keepachangelog.com/en/1.0.0/ for examples -->

  ### 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

ACKs for top commit:
  ValuedMammal:
    ACK 1a4d5cf2c5271b722e115492557643dcab22df3f
  notmandatory:
    ACK 1a4d5cf2c5271b722e115492557643dcab22df3f

Tree-SHA512: e693baeea112dffa12ccc576271f38f3188dc24669a70af7196e33e5eea08c5d82940792330682b8a4b1ec48ef98e1cbaa2f713736f393555744fdf44d79a26a