update python build to comply with PEP 660

[patrick-schultz]

PEP 660 standardizes a method of installing editable python packages (meaning the package executes editable source files). pip is deprecating special handling of the old setuptools based method. See this issue for details. It looks like the setup.py method is still supported, it's just not automatically discovered. Now it requires something in the pyproject.toml specifying the desired "install editable" method.