Add Python 3.13 support, drop 3.9

[greschd]

Remove the upper bound of the supported Python version, since that makes it tedious to add new versions: PyDPF Composites needs to be released before we can update PyACP, for example.

Add Python 3.13 to the explicitly supported versions in the trove classifiers, and add it to the test matrix.

Drop support for Python 3.9.

Run pyupgrade with the --py310-plus flag, and remove the now unused imports.

[wiz-inc-572fc38784]

Wiz Scan Summary

Scanner	Findings
Vulnerabilities	1
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IaC Misconfigurations
Total	1

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.50746% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.49%. Comparing base (9ff7e3d) to head (832dbdd).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ites/server_helpers/_connect_to_or_start_server.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #546      +/-   ##
==========================================
- Coverage   91.53%   91.49%   -0.05%     
==========================================
  Files          50       50              
  Lines        3355     3350       -5     
==========================================
- Hits         3071     3065       -6     
- Misses        284      285       +1     

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[greschd]

Waiting on a release of PyVista which does not lock VTK to <9.4.0. We could pin an older PyVista, but that's not worth it IMO.