Function rf_mul_unreduced 

unsafe fn rf_mul_unreduced(
    m: __m128i,
    h: __m128i,
    d: __m128i,
) -> (__m128i, __m128i)

R/F multiplication using 4 CLMULs per block

Given M = [M1 : M0] and precomputed H = [H1 : H0], D = [D1 : D0]:

• R = M0×D1 ⊕ M1×H1 (2 CLMULs)
• F = M0×D0 ⊕ M1×H0 (2 CLMULs)

Returns (R, F) for later reduction