pkg_resources becoming deprecated

[samberry19]

Hi! I installed the latest development version of evcouplings and I get this warning:

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.
  from pkg_resources import resource_filename

Just a reminder to fix this before December or it looks like it could be a problem!

[thomashopf]

Thanks @samberry19 for the notice, will make sure to change this