Build a shared wheel once in the test suite

This cuts the setup times for tox environments roughly in half,
and reduces `tox p` invocations from ~18s to ~14s.

Author: kurtmckee

CHANGELOG.rst

@@ -17,6 +17,7 @@ Fixed
 - Improve typing/logic for `options` in decode, decode_complete by @pachewise in `#1045 <https://github.com/jpadilla/pyjwt/pull/1045>`__
 - Declare float supported type for lifespan and timeout by @nikitagashkov in `#1068 <https://github.com/jpadilla/pyjwt/pull/1068>`__
 - Fix ``SyntaxWarning``\s/``DeprecationWarning``\s caused by invalid escape sequences by @kurtmckee in `#1103 <https://github.com/jpadilla/pyjwt/pull/1103>`__
+- Development: Build a shared wheel once to speed up test suite setup times by @kurtmckee in `#1114 <https://github.com/jpadilla/pyjwt/issues/1114>`__
 
 Added
 ~~~~~

tox.ini

@@ -35,6 +35,10 @@ isolated_build = True
 
 
 [testenv]
+# Build a shared wheel once, rather than building a .tar.gz file
+# and forcing each individual tox environment to convert it to a wheel.
+package = wheel
+wheel_build_env = build_wheel
 # Prevent random setuptools/pip breakages like
 # https://github.com/pypa/setuptools/issues/1042 from breaking our builds.
 setenv =