Update test management with tox and supported Python versions

[davidpirogov]

Description

The existing code uses language features from Python 3.10 and above.

The existing Python 3.8 tests were not consistently triggered in the test suite, hence they intermittently passed or were skipped.

Python 3.8 and Python 3.9 are End of Life. See https://devguide.python.org/versions/ for dates.

Additionally, the syntax changes with 3.10 means that modern linting fails the tests.

We need to support from Python 3.10 up to 3.14 / 3.14t which are the current stable production versions.

This PR adds tox package, which automates running existing tests in multiple Python versions.

This is done via uv run tox.

Additional changes include updating Github Actions workflows to also check uv run ruff check . and uv run mypy src/toon_format

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (we did not need to add 3.8 and 3.9 into our support schedule)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Related Issues

Related to #23

Changes Made

• Added tox
• Updated Publishing guide
• Updated Github Actions to use correct uv commands (rather than pip)
• Set Python 3.14 as the static linter test and code coverage