task(python_v): support Python 3.10 and 3.11, release 0.3.0

[mysiar]

What

Widens the supported Python range from >=3.12 to >=3.10 and releases it as 0.3.0.

• requires-python in pyproject.toml: >=3.12 -> >=3.10
• Test workflow matrix now covers 3.10, 3.11, 3.12 and 3.13
• CHANGELOG.md: new 0.3.0 section, and 0.2.0 given its release date

Why 0.3.0 and not 0.2.1

Widening requires-python adds capability: the package now installs where it previously refused. Semantic Versioning puts backward-compatible new functionality in the MINOR position, and 0.2.0 is already published on PyPI. A patch release would understate the change for anyone reading the version alone.

Testing

The GitHub Actions tests workflow passes on all four versions in the matrix. Python 3.9 was tried and dropped: the codebase uses PEP 604 unions (int | None), which need 3.10 or newer.

Note for review

[tool.ruff] target-version in pyproject.toml still reads py312. Ruff therefore lints against 3.12 syntax rules and will not flag code that breaks on 3.10. Worth setting to py310 to match requires-python, either here or as a follow-up.