🧮 Add SUM() excellent function

[rowanseymour]

Adds #1015

[codecov]

Codecov Report

Merging #1020 (946ef36) into main (a4f0335) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1020      +/-   ##
==========================================
+ Coverage   86.76%   86.77%   +0.01%     
==========================================
  Files         237      237              
  Lines       10355    10365      +10     
==========================================
+ Hits         8984     8994      +10     
  Misses        955      955              
  Partials      416      416              

Impacted Files	Coverage Δ
excellent/functions/builtin.go	97.91% <100.00%> (+0.03%)	⬆️

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