lasers/mirrors do not work properly about cs7038 HOT 1 CLOSED

After some research I find the bug lies in Physics2D.Raycast().
Instead of detecting collision tile by tile (like in Troley.Push()), I used only one Physics2D.Raycast() per laser segment to find collision in front of it.
But this method somehow misses some collision. I find it only works for some columns and doesn't work for others.
== Solution
Before finding the essential reason of missing collision detection, I solve this problem temporarily by adding Physics2DExt class to replace Physics2D when searching collision in one direction. Basically it uses the method in Troley (detecting collision tile by tile). We may use it in Troley.Push() as well to avoid a potential bug (infinite loop).

from cs7038.