Objective

#527 used a read-only UnsafeWorldCell for the initialization of ColliderAabb in an on_add hook for Collider. However, it uses methods that provide mutable access, which is unsafe and panics with debug assertions.

Solution

Remove the whole AABB initialization logic and use of unsafe. Having it didn't make sense since the initial positions are likely wrong anyway.

ColliderAabb is now explicitly specified to be ColliderAabb::INVALID until the first physics update.