reduce cyclomatic complexity of builtins

[ichiban]

No description provided.

[codecov-commenter]

Codecov Report

Merging #130 (c47ebac) into main (fc785d9) will increase coverage by 3.25%.
The diff coverage is 95.05%.

@@            Coverage Diff             @@
##             main     #130      +/-   ##
==========================================
+ Coverage   85.69%   88.95%   +3.25%     
==========================================
  Files          18       18              
  Lines        5083     5050      -33     
==========================================
+ Hits         4356     4492     +136     
+ Misses        646      484     -162     
+ Partials       81       74       -7     

Impacted Files	Coverage Δ
engine/builtin.go	90.41% <93.97%> (+7.15%)	⬆️
engine/stream.go	100.00% <100.00%> (ø)

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