Drop support for Python 3.9 and require 3.10 minimum

[tleonhardt]

Drop support for Python 3.9 and require 3.10 minimum.

Python 3.9 hits EOL for security updates in October 2025 - in about 2 months. Version 3.0.0 of cmd2 will likely be out sometime in September or October, about the time same time 3.9 hits EOL.

The primary change applies in this PR automatically by ruff is that type hints now support the | opertor and both Optional and Union are needed much less frequently from the typing module.

Moving to 3.10 minimum also opens up the door to begin using features like structural pattern matching in new code and/or code refactoring.

Also:

• Upgrade versions of ruff and prettier used by pre-commit

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.75%. Comparing base (5ac81d4) to head (1383b1a).
⚠️ Report is 100 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1473      +/-   ##
==========================================
- Coverage   98.77%   98.75%   -0.02%     
==========================================
  Files          21       21              
  Lines        5878     5874       -4     
==========================================
- Hits         5806     5801       -5     
- Misses         72       73       +1     

Flag	Coverage Δ
unittests	98.75% <100.00%> (-0.02%)	⬇️

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