Promotions Percent Calculator: Allow fractional percent

[mamhoff]

Summary

Prior to this, it was not possible to create a calculator with e.g. 12.5 percent.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.35%. Comparing base (d070f94) to head (d6b3df0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6330   +/-   ##
=======================================
  Coverage   89.35%   89.35%           
=======================================
  Files         961      961           
  Lines       20195    20195           
=======================================
  Hits        18046    18046           
  Misses       2149     2149           

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