fix: Use importlib-resources over deprecated pkg_resources

[matthewfeickert]

Resolves #50

• Add importlib-resources as an install dependency for Python 3.8 as Python 3.12 deprecates and removes pkg_resources.
• Replace use of pkg_resources.resource_filename with importlib.resources.files for Python 3.9+ and importlib_resources.files for Python 3.8.
• Apply isort.
• Note import order issue to be fixed.

* Add importlib-resources as an install dependency for Python 3.8 as Python 3.12 deprecates
  and removes pkg_resources.
* Replace use of pkg_resources.resource_filename with importlib.resources.files
  for Python 3.9+ and importlib_resources.files for Python 3.8.
* Apply isort.
* Note import order issue to be fixed.