Function gpu_sphere_collision 

pub fn gpu_sphere_collision(
    spheres: &[Sphere],
    pairs: &[(usize, usize)],
) -> Vec<SphereContact>

Test sphere-sphere collisions for the given pairs (mock GPU narrowphase).

For each pair (i, j) in pairs, tests whether spheres i and j overlap and, if so, computes a SphereContact.

Arguments

• spheres - Sphere descriptors, indexed by object id.
• pairs - Candidate pairs from the broadphase.