feat: run integration tests on more platforms

[Molter73]

Description

Add support for running integration tests on Python 3.9 through 3.14+ with minimal changes using modern Python features.

Changes:

• event.py: Add future annotations import to enable modern type hint syntax (int | None) on Python 3.9, with fallback for @OverRide decorator (Python 3.12+)
• test_config_hotreload.py: Handle both builtin TimeoutError (Python 3.11+) and concurrent.futures.TimeoutError (Python 3.9-3.10)
• test_path_rmdir.py: Reverse event order for Python < 3.10 due to different shutil.rmtree deletion ordering

This avoids using deprecated Union/Optional types while maintaining backward compatibility.

Assisted-by: Claude Code (claude-sonnet-4-5@20250929)

Checklist

• Patch has a change log entry OR does not need one.
• Investigated and inspected CI test results
• Updated documentation accordingly

Automated testing

• Added unit tests
• Added integration tests
• Added regression tests

If any of these don't apply, please comment below.

Testing Performed

Tested: 102 tests pass on Python 3.9.25

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✨ Finishing Touches

🧪 Generate unit tests (beta)

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 27.96%. Comparing base (5310516) to head (33ec932).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #760   +/-   ##
=======================================
  Coverage   27.96%   27.96%           
=======================================
  Files          21       21           
  Lines        2596     2596           
  Branches     2596     2596           
=======================================
  Hits          726      726           
  Misses       1867     1867           
  Partials        3        3           

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