Function safe_arch::add_m256d

#[must_use]pub fn add_m256d(a: m256d, b: m256d) -> m256d

This is supported with target feature avx only.

Lanewise a + b with f64 lanes.

let a = m256d::from_array([1.0, 2.0, 3.0, 4.0]);
let b = m256d::from_array([5.0, 6.0, 7.0, 8.5]);
let c = add_m256d(a, b).to_array();
assert_eq!(c, [6.0, 8.0, 10.0, 12.5]);