feat: frontend optimizations

[charles-cooper]

What I did

a couple compilation-time optimizations. bring total time down by 5% (vyper -f bytecode), and time in frontend code down by 20% (vyper -f annotated_ast).

How I did it

cache VyperNode.get_fields(), it's a hotspot
optimize get_common_types, the line rejected = [i for i in common_types if i not in common] is a hotspot

How to verify it

Commit message

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Description for the changelog

Cute Animal Picture

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4b4e188) 84.98% compared to head (b9dec91) 84.99%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3781   +/-   ##
=======================================
  Coverage   84.98%   84.99%           
=======================================
  Files          92       92           
  Lines       13709    13714    +5     
  Branches     3077     3079    +2     
=======================================
+ Hits        11651    11656    +5     
  Misses       1570     1570           
  Partials      488      488           

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