ci: add testing against Python 3.14

[DanielEScherzer]

Description

Add Python 3.14 to the GitHub Actions testing matrix.

Motivation and context

Python 3.14 was released last month, and I'd like to confirm that this package works with Python 3.14 before I upgrade.

How has this been tested?

Testing done with GitHub Actions.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

PR checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• I have added tests to cover my changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (fbf1867) to head (e860aa8).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##                main       #50   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        27        27           
===========================================
  Files              2         2           
  Lines             83        79    -4     
===========================================
- Hits              83        79    -4     

see 2 files with indirect coverage changes

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[ramsey]

Thank you for contributing! 🎉