Improve overall api usage

[pietzschke]

Checklist for your PR

• please start with a draft PR and mark it as ready for review when you are confident that your implementation works as expected.
• add a changelog entry in CHANGELOG.md with a link to this PR.
• make sure that all tests pass and add new test functions if your code is not covered by existing tests. Please use mock tests when network requests are required.
• let someone review & approve your code, make changes where necessary.

Hints

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[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (b5ead78) 87.31% compared to head (e7d0c96) 87.40%.
Report is 2 commits behind head on master.

❗ Current head e7d0c96 differs from pull request most recent head a5bff98. Consider uploading reports for the commit a5bff98 to get more accurate results

Files	Patch %	Lines
src/personio_py/mapping.py	86.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
+ Coverage   87.31%   87.40%   +0.09%     
==========================================
  Files           7        7              
  Lines         946      961      +15     
==========================================
+ Hits          826      840      +14     
- Misses        120      121       +1     

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