Update to avoid pkg_resources deprecation warning (Setuptools 81+)

[Anthony-DE-FARIA]

Hi,

We're encountering a deprecation warning from pkg_resources when using python-anvil with recent versions of Setuptools:

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.

Would you consider updating the codebase to use the modern importlib API ?

Thanks for your work on this library!