wip,draft: Add async support to persist_test_utils

[ValuedMammal]

Description

Expands persist_test_utils module by adding a function persist_wallet_changeset_async to be used for testing an AsyncWalletPersister implementation. For now this is still WIP.

Notes to the reviewers

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 0% with 158 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.39%. Comparing base (36f98df) to head (d6f2cdc).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
src/persist_test_utils.rs	0.00%	158 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #343      +/-   ##
==========================================
- Coverage   84.81%   83.39%   -1.42%     
==========================================
  Files          23       23              
  Lines        8145     8395     +250     
==========================================
+ Hits         6908     7001      +93     
- Misses       1237     1394     +157     

Flag	Coverage Δ
rust	83.39% <0.00%> (-1.42%)	⬇️

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