setup: migrate from distutils

distutils is starting to get removed from the standard library since
2020 and has been phased out since 2014 (or earlier). Distutils has
been exposed only recently, so relatively old Python (like 3.8)
setuptools doesn't have them yet.

1. https://peps.python.org/pep-0632
2. pypa/setuptools@974dbb0

Part of #270

Author: DifferentialOrange

setup.py

@@ -6,12 +6,8 @@
 import codecs
 import os
 
-try:
-    from setuptools import setup, find_packages
-    from setuptools.command.build_py import build_py
-except ImportError:
-    from distutils.core import setup, find_packages
-    from distutils.command.build_py import build_py
+from setuptools import setup, find_packages
+from setuptools.command.build_py import build_py
 
 # Extra commands for documentation management
 cmdclass = {}

test/setup_command.py

@@ -4,10 +4,15 @@
 """
 
 import unittest
-from distutils.errors import DistutilsError
 
 import setuptools
 
+try:
+    from setuptools.errors import BaseError
+except ModuleNotFoundError:
+    # pylint: disable=deprecated-module
+    from distutils.errors import DistutilsError as BaseError
+
 class Test(setuptools.Command):
     """
     Class implementing `python setup.py test`.
@@ -37,4 +42,4 @@ def run(self):
         test_runner = unittest.TextTestRunner(verbosity=2)
         result = test_runner.run(tests)
         if not result.wasSuccessful():
-            raise DistutilsError('There are failed tests')
+            raise BaseError('There are failed tests')