Type Alias EmptyShape

Empty shape - has no volume, no collision geometry. Used for anchor points in constraints or as placeholders.

EmptyShape bodies:

• Do not produce any collision contacts (no-op collision/cast functions)
• Have zero mass and zero inertia
• Have zero-size AABB
• Are added to broadphase but filtered out during narrowphase via dispatch
• Can still be used in constraints (e.g., for "fixed to world" constraints)