Sculk Spreads Underground

Sculk should be able to spread underground if the room it is in is full of sculk. For example, when there's a field of sculk, the sculk will spread downwards from the center of the cluster, making it able to breach underground bases, or when the sculk takes up an entire room it should push outward from the walls and spread more. This gives the sculk a more dangerous feel, and makes it harder to contain.