Need to migrate away from pkg_resources

[jotelha]

Python 3.12 now warns

/home/jotelha/venv-python-3.12/lib/python3.12/site-packages/dtool_cli/cli.py:6: UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
  from pkg_resources import iter_entry_points

We have already fixed this in other packages. We should fix this here ASAP.