Function integrate_angular_velocity_only 

pub fn integrate_angular_velocity_only(
    states: &mut [RigidBodyState],
    torques: &[[f64; 3]],
    dt: f64,
)

Integrate only the angular velocity of each body (no linear dynamics).

This mimics a GPU kernel that handles only rotational degrees of freedom — useful when linear and angular integration are split into separate passes.