Drop Python 3.9 support when it goes EOL

### Description of issue

When Python 3.9 goes EOL In October 2025, we should drop support for it.
As part of this, we should also drop our usage of the `pkg_resources` module, which is part of `setuptools`, and not a built-in module.

When we added support for Python 3.12, we shifted toward using the built-in `importlib.metdata` module, instead.