[Test PR] Multi-Keychain Wallets

[thunderbiscuit]

This is more of a test PR to try and see if I can make simpler #318 by approaching it completely differently, i.e. not with a lot of small commits that are really hard to rebase but rather a few, much bigger commits that concern specific areas of the codebase.

Changelog notice

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran just p before pushing

New Features:

• I've added tests for the new feature
• 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
• I'm linking the issue being fixed by this PR

[codecov]

Codecov Report

❌ Patch coverage is 75.42533% with 130 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.89%. Comparing base (8f8a8e9) to head (6f924d1).

Files with missing lines	Patch %	Lines
src/wallet/persisted.rs	26.08%	34 Missing ⚠️
src/persist_test_utils.rs	71.42%	32 Missing ⚠️
src/keyring/error.rs	10.71%	25 Missing ⚠️
src/keyring/mod.rs	91.07%	15 Missing ⚠️
src/wallet/params.rs	56.00%	11 Missing ⚠️
src/wallet/changeset.rs	72.41%	8 Missing ⚠️
src/descriptor/error.rs	0.00%	2 Missing ⚠️
src/keyring/changeset.rs	98.97%	1 Missing ⚠️
src/types.rs	90.90%	1 Missing ⚠️
src/wallet/tx_builder.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #367       +/-   ##
===========================================
- Coverage   85.33%   61.89%   -23.45%     
===========================================
  Files          24       25        +1     
  Lines        8335     4461     -3874     
===========================================
- Hits         7113     2761     -4352     
- Misses       1222     1700      +478     

Flag	Coverage Δ
rust	61.89% <75.42%> (-23.45%)	⬇️

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