Resolve CWG-43 and CWG-42 by applying tox 4 compatability.

setup.cfg

@@ -29,7 +29,7 @@ include_package_data = true
 packages = find:
 python_requires = >=3.7
 install_requires =
-    importlib-metadata>=0.12;python_version<"3.8"
+    importlib-metadata>=0.12, <5.0;python_version<"3.8"
     numpy
 
 [flake8]

tox.ini

@@ -2,11 +2,12 @@
 # Generative environment list to test all supported Python versions
 envlist = py3{7,8,9,10},black,pep8,pylint
 minversion = 3.18.0
-# Source distributions are explicitly build using tox -e build
-skipsdist = True
 
 [testenv]
 usedevelop = True
+package = wheel
+wheel_build_env = .pkg
+
 setenv =
     LANGUAGE=en_US
     LC_ALL=en_US.UTF-8