scripts/test.py: allow use on github for releases etc.

Things for github:
* -a: optionally reads command-line args from a specified environment variable.
  This will simplify use on Github, especially to work around the 10-parameter
  limit in workflows.
* -o: specifies what platforms to run on - if no match we do nothing.

Other:
* new command `cibw` build wheels with cibuildwheel.
* new command `wheel` builds wheel and installs.

Author: julian-smith-artifex-com