fix(proxy):apply saved proxy config to electrum, esplora and cbf

[tvpeter]

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

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

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[codecov]

Codecov Report

❌ Patch coverage is 95.34884% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.24%. Comparing base (5afbc8a) to head (f519a04).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/client.rs	86.66%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #329      +/-   ##
==========================================
+ Coverage   57.78%   59.24%   +1.46%     
==========================================
  Files          22       23       +1     
  Lines        3733     3857     +124     
==========================================
+ Hits         2157     2285     +128     
+ Misses       1576     1572       -4     

Flag	Coverage Δ
rust	59.24% <95.34%> (+1.46%)	⬆️

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