Remove support for EOL Python 3.9

[adtzlr]

Also:

• fix old years in LICENSE, docs/index.rst and README.md
• test with Python 3.10 and 3.13 (3.14 works but has no VTK wheel ready at PyPI - avoid the extra index url)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.41%. Comparing base (6b5f4de) to head (91c2810).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1026   +/-   ##
=======================================
  Coverage   97.41%   97.41%           
=======================================
  Files         185      185           
  Lines        7029     7029           
=======================================
  Hits         6847     6847           
  Misses        182      182           

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