pub fn sandwich_point(m: Motor, p: [f32; 3]) -> [f32; 3]
Null-vector sandwich on euclidean (x, y, z) — P' = Ω P Ω̃.
(x, y, z)
P' = Ω P Ω̃
P = e₀ + x·e₁ + y·e₂ + z·e₃. When m.d == 0, ε terms vanish → pure rotation.
P = e₀ + x·e₁ + y·e₂ + z·e₃
m.d == 0