string goes object

[ludwiglierhammer]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes no current issue
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• CHANGELOG.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• adapt to new pandas version (>=3.0.0) that makes huge differences between string and object types.

Does this PR introduce a breaking change?

• reader functions return object types instead of string types

Other information:

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.05%. Comparing base (98ad9c4) to head (0e1caf4).
⚠️ Report is 24 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #435      +/-   ##
==========================================
+ Coverage   96.69%   97.05%   +0.35%     
==========================================
  Files          80       78       -2     
  Lines        3817     3496     -321     
==========================================
- Hits         3691     3393     -298     
+ Misses        126      103      -23     

Flag	Coverage Δ
unittests	97.05% <100.00%> (+0.35%)	⬆️

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