Don't generate AssistedFactory for unsupported variants

[bacecek]

This is a cherry-pick of #210 to main branch

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.65%. Comparing base (727acad) to head (f6a0e5c).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #211      +/-   ##
============================================
- Coverage     84.27%   83.65%   -0.62%     
+ Complexity     1662     1661       -1     
============================================
  Files           200      200              
  Lines          8647     7967     -680     
  Branches       1516     1517       +1     
============================================
- Hits           7287     6665     -622     
+ Misses          818      760      -58     
  Partials        542      542              

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