Add list type safety, helpers; remove cruft

[drew-512]

No description provided.

[codecov]

Codecov Report

Merging #157 (2ee3956) into master (3068cb5) will decrease coverage by 0.02%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##           master     #157      +/-   ##
==========================================
- Coverage   74.55%   74.53%   -0.03%     
==========================================
  Files          64       64              
  Lines       11187    11190       +3     
==========================================
- Hits         8341     8340       -1     
- Misses       2297     2301       +4     
  Partials      549      549              

Impacted Files	Coverage Δ
py/traceback.go	22.22% <ø> (-2.11%)	⬇️
py/list.go	62.86% <33.33%> (-1.24%)	⬇️
py/dict.go	77.31% <100.00%> (+0.23%)	⬆️

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[sbinet]

LGTM