Wagtail 7.2 maintenance

[nickmoreton]

This pull request updates the project's Python and Wagtail version support.

Python and Wagtail version support:

• Added support for Python 3.14 in the test matrix (.github/workflows/tests.yml, tox.ini) and set it as the default language version for pre-commit hooks (.pre-commit-config.yaml).
• Updated minimum required Wagtail version to 6.3 in setup.cfg and setup.py, and added support for Wagtail 7.2

Development and testing dependencies:

• Upgraded development dependencies: black to 25.11.0, flake8 to 7.3.0, and isort to 7.0.0 in both setup.py and .pre-commit-config.yaml.

Documentation and changelog:

• Updated CHANGELOG.md to document the addition of Wagtail 7.2 support in tox testing and classifiers.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.68%. Comparing base (bce562a) to head (5d0b171).
⚠️ Report is 32 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #31      +/-   ##
==========================================
+ Coverage   73.33%   73.68%   +0.35%     
==========================================
  Files           5        5              
  Lines          75       76       +1     
==========================================
+ Hits           55       56       +1     
  Misses         20       20              

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