Cope with Python 3.12

[srmainwaring]

Replace use of deprecated packages that are removed in Python 3.12.

https://importlib-resources.readthedocs.io/en/latest/migration.html

• replace pkg_resources.resource_filename with importlib_resources.files and importlib_resources.as_file

Tasks

• [ ] manage import for Python versions < 3.7.
• [ ] confirm backwards compatibility.

[tridge]

i've merged a smaller change that gets 3.12 working