feat: more frontend optimizations

[charles-cooper]

What I did

How I did it

How to verify it

Commit message

- optimize `VyperNode.get_descendants()` and `get_children()`
- get rid of `sort_nodes()`, we can guarantee ordering the old fashioned
  way (topsort)
- optimize `VyperNode.__hash__()` and `VyperNode.__init__()`
- optimize `IntegerT.compare_type()`

optimizes front-end compilation time by another 25%

Description for the changelog

Cute Animal Picture

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2d2a682) 84.99% compared to head (01ec986) 84.98%.
Report is 1 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3785      +/-   ##
==========================================
- Coverage   84.99%   84.98%   -0.02%     
==========================================
  Files          92       92              
  Lines       13717    13717              
  Branches     3079     3077       -2     
==========================================
- Hits        11659    11657       -2     
- Misses       1570     1571       +1     
- Partials      488      489       +1     

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