refactor: to `timezone` specific `datetime` helpers to avoid use deprecated functions

[bednar]

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Proposed Changes

Checklist

• [x] CHANGELOG.md updated
• [x] Rebased/mergeable
• [x] Tests pass
• [x] Commit messages are conventional
• [x] Sign CLA (if not already signed)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 53.39%. Comparing base (c580008) to head (4da8d38).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #86      +/-   ##
==========================================
+ Coverage   50.52%   53.39%   +2.86%     
==========================================
  Files          39       40       +1     
  Lines        2276     2285       +9     
==========================================
+ Hits         1150     1220      +70     
+ Misses       1126     1065      -61     

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