Replace custom `__getattr__` method with explicit attribute setting for group names

[codecov[bot]]

Codecov Report

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

Project coverage is 90.44%. Comparing base (907ee8f) to head (aad1b9a). Report is 1 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #189 +/- ## ========================================== + Coverage 90.23% 90.44% +0.21% ========================================== Files 14 14 Lines 1352 1361 +9 ========================================== + Hits 1220 1231 +11 + Misses 132 130 -2 ```

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