Fix severe perf regression of complex nested function calls

[JohnnyMorganz]

Fixes #477

[codecov]

Codecov Report

Merging #478 (4dfcd0e) into master (97c4b53) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #478   +/-   ##
=======================================
  Coverage   97.48%   97.49%           
=======================================
  Files          14       14           
  Lines        4978     4994   +16     
=======================================
+ Hits         4853     4869   +16     
  Misses        125      125           

Impacted Files	Coverage Δ
src/formatters/functions.rs	98.61% <100.00%> (+0.01%)	⬆️
src/shape.rs	98.41% <100.00%> (+0.13%)	⬆️

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[JohnnyMorganz]

Performance is still not 100% where we want it to be, but this is a big improvement