[FEATURE] Implement `PaymentAttemptInterface` for `MockDb`

Spin out from #172. Please refer to that issue for more information.
<think>
PR Context:
- Title: Implement PaymentAttemptInterface for MockDb
- Merged: None
- Files changed: 1 files
- Commits: 1 commits

Implementation approach:
Fixes #1329


</think>

To implement this, you'll need to modify:


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