refactor: separate build, test, and deploy in Python workflow (#2308)

_Test what you build, deploy what you test._

This refactors the Python CI workflow to wait for _all_ tests to pass
before publishing photonlibpy to PyPI.

- build-python-examples reuses the built wheel, removes redundant builds
- Simplify run.sh to not rebuild wheel since it's already installed

photonlib-python-examples/run.sh

@@ -5,19 +5,6 @@ if [ $# -eq 0 ]
     exit 1
 fi
 
-# To run any example, we want to use photonlib out of this repo
-# Build the wheel first
-pushd ../photon-lib/py
-if [ -d build ]
-  then rm -rdf build
-fi
-python3 setup.py bdist_wheel
-popd
-
-# Add the output directory to PYTHONPATH to make sure it gets picked up
-export PHOTONLIBPY_ROOT=../photon-lib/py
-export PYTHONPATH=$PHOTONLIBPY_ROOT
-
 # Move to the right example folder
 cd $1