refactor: to timezone specific datetime helper to avoid use deprecated functions

[bednar]

Closes #603

Proposed Changes

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• pytest tests completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.43%. Comparing base (b844a82) to head (e205347).
Report is 10 commits behind head on master.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #652   +/-   ##
=======================================
  Coverage   90.43%   90.43%           
=======================================
  Files          40       40           
  Lines        3524     3524           
=======================================
  Hits         3187     3187           
  Misses        337      337           

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[karel-rehor]

Tests and changed examples pass locally. Changes look correct. OK.