Build a wheel once

changelog.d/20230205_171012_kurtmckee_reduce_ci_usage.rst

@@ -0,0 +1,11 @@
+Changed
+.......
+
+-   Configure tox to build a wheel once.
+
+    This decreases CI total usage from ~20 minutes to ~15 minutes.
+    It decreases CI duration from ~10 minutes to ~7 minutes.
+
+    Tox's default behavior is to build a ``.tar.gz`` file.
+    However, pip will convert it to a ``.whl`` file prior to installation.
+    This results in a measurable decrease in performance on slow CI runners like Windows.

tox.ini

@@ -11,6 +11,8 @@ labels =
     ci-tests = py{37,38,39,310,311,py3}, py{37,311}-no_extras
 
 [testenv]
+package = wheel
+wheel_build_env = .pkg
 deps =
     -r{toxinidir}/requirements/test.txt
 extras =