🐛 fix state error in embed grouping calculation

[twentylemon]

Summary

Related to #1006. Logic there missed reseting the group variable. Dang ol' state.

Refactored the tests a bit when adding the new one. Changed the embed creation function to include the size so errors were easier to read, but it means there is no 0 length embed any more. /shrug.

Checklist

• [x] this is a source code change
  • [x] run format in the repository root
  • [x] run pytest in the repository root
  • [ ] link to issue being fixed using a fixes keyword, if such an issue exists
  • [ ] update the wiki documentation if necessary
• [ ] or, this is not a source code change

[codecov[bot]]

Codecov Report

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

Project coverage is 96.53%. Comparing base (3aee256) to head (62bdd6d). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1008 +/- ## ========================================== - Coverage 96.57% 96.53% -0.05% ========================================== Files 95 95 Lines 2251 2251 Branches 168 168 ========================================== - Hits 2174 2173 -1 - Misses 66 67 +1 Partials 11 11 ```

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