add examples to test suite

[jf---]

one of the most critical paths, example aren't under scrutiny from the testsuite
this is true for compas_viewer, but I'd argue for applying this where possible
in the fast paced world of compas for many examples are the gateway, hence covering these with pytest is a nice thing to do

(compas2) ➜  object git:(main) ✗ py robot.py
Traceback (most recent call last):
  File "/Users/jelle/Code/CADCAM/compas_viewer/docs/examples/object/robot.py", line 3, in <module>
    from compas_robots.viewer.scene.robotmodelobject import RobotModelObject
ModuleNotFoundError: No module named 'compas_robots.viewer'

[tomvanmele]

you are right, but we are refactoring the entire repo, and updating and testing the examples will be part of that...