Convert to a namespace package and upgrade GitHub actions

[JasperCraeghs]

1. The module will no longer clutter the namespace mlx. They have been moved to the subpackage mlx.robot2rst.
2. Convert the pkg_resources-style namespace package to a native namespace package
3. Remove support for Python 3.7
4. Test support for Python 3.12
5. Address deprecation warning about use of pkg_resources
6. Modernize the build system: Add a basic pyproject.toml

Closes #41

[JokeWaumans]

Sphinx 8 dropped support for Python 3.9, so the sphinx-latest test can only be executed on Python version higher than 3.9
FYI https://www.sphinx-doc.org/en/master/changes/8.0.html#release-8-0-0-released-jul-29-2024

[JokeWaumans]

The latest matplotlib requires Python>=3.10
https://github.com/matplotlib/matplotlib/blob/main/pyproject.toml#L43