Wagtail 72 maintenance

[nickmoreton]

Includes #54

This pull request updates the project's test matrix and dependencies to support newer versions of Python, Django, and Wagtail, and refreshes the development tooling.

Test matrix and compatibility updates:

• Expanded the test matrix in .github/workflows/test.yml and tox.ini to include Python 3.14 and Wagtail 7.2
• Updated Python version classifiers in setup.py to include Python 3.14

Development tooling updates:

• Upgraded testing and linting dependencies in setup.py to more recent versions: tox, coverage, flake8, and isort, improving reliability and compatibility with modern Python.
• Simplified the isort linting command in the Makefile by removing the deprecated --recursive flag.

Code style and imports:

• Cleaned up and reordered imports in tests/testapp/testapp/urls.py for better readability and consistency.