feat: parallel builds.

[knightedcodemonkey]

• Adds --parallel option for running the builds in parallel.

[codecov[bot]]

Codecov Report

Merging #10 (0a387f4) into main (6cfa904) will decrease coverage by 0.31%. The diff coverage is 92.42%.

@@            Coverage Diff             @@
##             main      #10      +/-   ##
==========================================
- Coverage   96.72%   96.41%   -0.31%     
==========================================
  Files           3        3              
  Lines         305      418     +113     
==========================================
+ Hits          295      403     +108     
- Misses         10       15       +5     

Files Changed	Coverage Δ
src/duel.js	93.90% <91.84%> (+0.75%)	:arrow_up:
src/init.js	100.00% <100.00%> (ø)

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