replace pkg_resources with importlib.resources

[bollwyvl]

Fixes increasingly loud warnings about the deprecation of pkg_resources, as seen on https://github.com/conda-forge/category_encoders-feedstock/pull/23

Proposed Changes

• replace use of pkg_resources with importlib.metadata
  • or importlib_metdata on python < 3.9
  • also removes an undeclared setuptools dependency, which is not technically stdlib

[PaulWestenthanner]

Looks good to me! Thanks for updating this!

[bollwyvl]

Thank you! There's a lot of FutureWarnings, too, but they are a little easier to handle. Maybe get to it another day...