Merge bitcoindevkit/bdk-cli#329: fix(proxy):apply saved proxy config to electrum...

Merge bitcoindevkit/bdk-cli#329: fix(proxy):apply saved proxy config to electrum, esplora and cbf

e8fc1e3ed10e351886b31cdd431fc4bda974aca0 fix(cli): use valid envt variable names for env fallbacks (Vihiga Tyonum)
2b4866a79cd3230963a66a20ab454721b1bfefec fix(client): Route cbf traffic via configured SOCKS5 proxy (Vihiga Tyonum)
f6a183f73963fce7aa6ece46153689a1eadea81e fix(client): route electrum & esplora traffic through config proxy (Vihiga Tyonum)

Pull request description:

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

  ### Description

  The application accepted SOCKS5 proxy options (--proxy, --proxy_auth, --retries, --timeout), persisted them to config.toml, and reloaded them on every subsequent run  but never applied them to any blockchain client. This PR updates the proxy options for electrum, esplora and cbf.

  Fixes #328

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

  ### Notes to the reviewers

  ## Changelog notice
  - Fixed routing electrum and esplora traffic through configured socks5 proxy
  - Routed compact filter (cbf) traffic through the configured SOCKS5 proxy
  - Rejected --proxy on the rpc backend, and unsupported proxy options (--proxy_auth, --timeout) on the rpc and cbf backends, instead of silently ignoring them

  <!-- 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-cli/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### Bugfixes:

  * [ ] 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:
  vadim-anfv:
    ACK e8fc1e3ed10e351886b31cdd431fc4bda974aca0

Tree-SHA512: 6f728ca4187c31282ae3d496d431279e7d16f1b093b83de1519ef63051e60f0ac24bbb04dcabb11e0458c56ff572a387c3742d1ca245fd83c7f6690f544a74cd