Get rid of pkg_resources dependency

[flying-sheep]

It has known performance problems and is in the process of being deprecated: pypa/setuptools-scm#513 (comment)

The time spent when importing dunamai is almost exclusively invested into pkg_resources:

$ PYTHONPROFILEIMPORTTIME=1 python -c 'import dunamai' 2>! importprofile.log
$ tuna importprofile.log

Alternatives

• pkg_resources.get_distribution(name).version → importlib.metadata.version(name) (https://docs.python.org/3/library/importlib.metadata.html)
• pkg_resources.parse_version(v) → packaging.version.Version(v) (https://packaging.pypa.io/en/latest/version.html)