fix: move set functions to a separate package

[Primetalk]

fix #96

[codecov]

Codecov Report

Base: 83.81% // Head: 83.20% // Decreases project coverage by -0.60% ⚠️

Coverage data is based on head (d81ff52) compared to base (1dfb49a).
Patch coverage: 53.33% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
- Coverage   83.81%   83.20%   -0.61%     
==========================================
  Files          37       38       +1     
  Lines        1835     1840       +5     
==========================================
- Hits         1538     1531       -7     
- Misses        259      271      +12     
  Partials       38       38              

Impacted Files	Coverage Δ
maps/maps.go	82.35% <0.00%> (-17.65%)	⬇️
slice/slice.go	83.03% <50.00%> (-6.14%)	⬇️
set/set.go	100.00% <100.00%> (ø)

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