pub fn mobius_add(a: &[f32], b: &[f32], curvature: f32) -> Vec<f32>
Möbius addition: the hyperbolic analog of vector addition.
a ⊕_c b = ((1 + 2c⟨a,b⟩ + c||b||²)a + (1 - c||a||²)b) / (1 + 2c⟨a,b⟩ + c²||a||²||b||²)