Add support for PEP 517.

[sebastic]

Using setup.py directly is deprecated.

[justb4]

Thanks, I need to understand first: so we keep setup.py ? Have not looked in a while, but am happy to make Stetl more current for builds and Pypi. I have seen uv but not yet tried. Do we need to change documentation as well?

[sebastic]

Thanks, I need to understand first: so we keep setup.py ?

Yes, setup.py is still a setuptools configuration file, see:

https://packaging.python.org/en/latest/discussions/setup-py-deprecated/

Have not looked in a while, but am happy to make Stetl more current for builds and Pypi.

The changes in this PR were motivated by the Debian packaging which can now use pybuild-plugin-pyproject instead of deprecated setup.py commands.

I have seen uv but not yet tried.

That seems like overkill for this project.

Project metadata can be moved from setup.py to pyproject.toml but there is no pressing need to do that.

Do we need to change documentation as well?

docs/install.rst could do with an update to not suggest to setup.py install, but I doubt any humans actually read that.

[justb4]

Ok, go.