move package setup from setup.py to pyproject.toml

[molpopgen]

Update the package configuration to current Python "standards":

• move as much as possible from setup.py to pyproject.toml.
• use setuptools_scm for auto-generating the package versions.
• Remove use of bdist_mpkg. This package creates "clickable" install files for macos. See here. Using this causes warnings in CI. It is also not necessary and possibly even undesirable. In most/all cases it would be preferable to build a wheel locally and then install that into a venv.

[molpopgen]

Need to look into the cause of these two messages during the Ubuntu CI:

 ImportError while trying to load entry-point bdist_mpkg: cannot import name 'Plist' from 'plistlib' (/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/plistlib.py)
ERROR setuptools_scm._file_finders.git listing git files failed - pretending there aren't any

[molpopgen]

If this PR is merged, then the docs will want to remove mentions of python setup.py because any given env may not be ready for it.

For example, to make an editable/development install/build:

python setup.py build_ext -i

becomes

python -m pip install -e .

And python setup.py bdist_wheel would probably be replaced with python -m build -w . (which requires python -m pip install build).

Etc..

[apragsdale]

Thanks @molpopgen - this is really helpful!