Move code to src

[alifbe]

Move code into src and upgrade version for actions/setup-python

Close #424

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c55ed28) 98.80% compared to head (cf8c8c8) 98.80%.

❗ Current head cf8c8c8 differs from pull request most recent head a634334. Consider uploading reports for the commit a634334 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #432   +/-   ##
=======================================
  Coverage   98.80%   98.80%           
=======================================
  Files          17       17           
  Lines        2682     2682           
=======================================
  Hits         2650     2650           
  Misses         32       32           

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