Add support for python 3.14

py2app does not support free-threaded python

It is no longer possible to use an install_requires
option when invoking py2app.

Support for this was inherited from setuptools, and
that feature has been deprecated for a long time at
this point.

Don't use pkg_resources

The codebase still falls back to using pkg_resources
for ancient versions of Python, but should no longer
use this library for versions that are still
in support.