allow modern setuptools without pkg_resources

[dimpase]

pkg_resources is deprecated, and removed in the latest Setuptools. Thus their use has to be replaced, following e.g. recommendations in https://setuptools.pypa.io/en/latest/pkg_resources.html

Without this patch, one gets

$ python3
Python 3.13.9 (main, Oct 25 2025, 23:32:23) [GCC 15.2.1 20251018] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cl4py
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    import cl4py
  File "/home/dima/tmp/.venv/lib/python3.13/site-packages/cl4py/__init__.py", line 2, in <module>
    from .lisp import Lisp
  File "/home/dima/tmp/.venv/lib/python3.13/site-packages/cl4py/lisp.py", line 6, in <module>
    from pkg_resources import resource_filename
ModuleNotFoundError: No module named 'pkg_resources'
>>>