fix: replace lodash set with immutable version

[KaneFreeman]

Fixes #937

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[codecov]

Codecov Report

Merging #940 (6d07cb4) into main (7ec1548) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #940      +/-   ##
==========================================
+ Coverage   52.26%   52.28%   +0.01%     
==========================================
  Files         230      231       +1     
  Lines        9882     9885       +3     
  Branches     2585     2585              
==========================================
+ Hits         5165     5168       +3     
  Misses       4332     4332              
  Partials      385      385              

Files	Coverage Δ
packages/core/src/backend.ts	12.37% <100.00%> (ø)
packages/core/src/lib/formatters.ts	66.66% <100.00%> (ø)
packages/core/src/lib/i18n.ts	18.75% <100.00%> (ø)
packages/core/src/lib/util/set.util.ts	100.00% <100.00%> (ø)
packages/core/src/reducers/entries.ts	9.28% <100.00%> (ø)
packages/core/src/reducers/entryDraft.ts	26.71% <100.00%> (ø)