Add examples for scaling a robot.

# Feature Request

It would be nice to have an example showing how to load a robot from URDF / ROS (robot in meters) and then scale it (for millimeters).

```
robot = client.load_robot(load_geometry=True)
robot.artist = RobotArtist(robot.model)
robot.scale(1000)
```

It should also be ensured that `scale()` can be called before or after setting the artist, and lead to the same result.

Additionally, it should be clarified (eg in the documentation) whether `scale()` is idempotent or not, ie. calling `.scale(100)` twice in a raw causes twice the scaling (ie 10000) or is it idempotent in that multiple identical calls cause the same effect. Ideally, the call should be idempotent.