docs: add effigies as a contributor for code

[allcontributors]

Adds @effigies as a contributor for code.

This was requested by tsalo in this comment

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.54%. Comparing base (1c3f93e) to head (775818e).
Report is 63 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1004   +/-   ##
=======================================
  Coverage   89.54%   89.54%           
=======================================
  Files          26       26           
  Lines        3395     3395           
  Branches      619      619           
=======================================
  Hits         3040     3040           
  Misses        207      207           
  Partials      148      148           

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