Break dependency from setuptools

[gautierrog]

In modern python setups, dependencies to setuptools are deprecated. Here is the contribution to break it.

It fixes issues like these

File "/venv/lib/python3.13/site-packages/marshmallow_jsonschema/__init__.py", line 1, in <module>
    from pkg_resources import get_distribution
ModuleNotFoundError: No module named 'pkg_resources'