refactor: Delegate rusqlite::Connection persister to transaction persister

[shinigami-777]

Description

Issue: #279
The WalletPersister implementations for rusqlite::Connection and rusqlite::Transaction are currently independent. The connection persister just creates a new transaction, does what the transaction persister does, and then commits. This refactor removes that duplication by having the Connection impl delegate directly to the Transaction impl.

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.17%. Comparing base (4e202c8) to head (5415d0c).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #421      +/-   ##
==========================================
+ Coverage   80.04%   80.17%   +0.13%     
==========================================
  Files          24       24              
  Lines        5336     5336              
  Branches      242      242              
==========================================
+ Hits         4271     4278       +7     
+ Misses        987      980       -7     
  Partials       78       78              

Flag	Coverage Δ
rust	80.17% <100.00%> (+0.13%)	⬆️

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[ValuedMammal]

LGTM