feat: relax FindKeyBy constraint

[powerman]

Fixes #204

[codecov-commenter]

Codecov Report

Merging #205 (1d3ca41) into master (cf45927) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #205   +/-   ##
=======================================
  Coverage   90.62%   90.62%           
=======================================
  Files          13       13           
  Lines        1557     1557           
=======================================
  Hits         1411     1411           
  Misses        143      143           
  Partials        3        3           

Flag	Coverage Δ
unittests	90.62% <100.00%> (ø)

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Impacted Files	Coverage Δ
find.go	100.00% <100.00%> (ø)

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[samber]

Gosh! I suppose It was a copy from lo.FindKey that needs a comparable type.

Thanks for the bug report!