feat: re-add ability to customize box shadow size

[Techassi]

I was a little to eager to move all .shadow-x size classes to statically defined classes. This removed the ability to customize / extend box shadow sizes like #593 (comment) mentions.

This PR re-adds this functionality and also enables it to be used alongside the new colored box shadows.

[codecov-commenter]

Codecov Report

Merging #631 (74c9484) into main (ebd5f1d) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #631      +/-   ##
==========================================
+ Coverage   88.16%   88.17%   +0.01%     
==========================================
  Files          57       57              
  Lines        4850     4855       +5     
  Branches     1032     1034       +2     
==========================================
+ Hits         4276     4281       +5     
  Misses        311      311              
  Partials      263      263              

Impacted Files	Coverage Δ
src/config/base.ts	75.00% <ø> (ø)
src/lib/utilities/static.ts	100.00% <ø> (ø)
src/utils/completions.ts	100.00% <ø> (ø)
src/lib/utilities/dynamic.ts	94.55% <100.00%> (+0.02%)	⬆️

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