Fix the raycast demo

[jecaro]

The raycast demo was currently failing with

loaded example raycast (7316KB free)
Traceback (most recent call last):
  File "main.py", line 12, in update
  File "///system/test.py", line 47, in update
  File "////system/tests/raycast.py", line 131, in update
TypeError: 'vec2' object isn't subscriptable

It looks like you want to call raycast here (credit to Claude for the finding). I also slowed down the loop a bit as it was running way too fast.