This modernizes kgb's packaging, moving from setup.py to

pyproject.toml. This maintains Python 2/3 compatibility, but allows us

to use modern pip to put this into an editable install and stay

compliant with modern Python practices.
The metadata has changed to now explicitly list Python 3.12 and 3.13 as

supported versions.

Successfully built source dists and wheels, verifying the package

contents and the Python 2/3 compatibility metadata.