refactor: singleton mixin

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.92%. Comparing base (6c633d5) to head (916235e). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #166 +/- ## ========================================== + Coverage 90.89% 90.92% +0.02% ========================================== Files 32 33 +1 Lines 1582 1587 +5 ========================================== + Hits 1438 1443 +5 Misses 144 144 ```

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