Remove deprecated `pkg_resources`

[jpn--]

Running ActivitySim currently warns:

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.

This package is imported in activitysim/cli/create.py, and in several tests. ActivitySim needs to be refactored to not use this deprecated package, in favor of importlib.resources, importlib.metadata and their backports (importlib_resources, importlib_metadata).