Function safe_arch::duplicate_even_lanes_m256

#[must_use]pub fn duplicate_even_lanes_m256(a: m256) -> m256

This is supported with target feature avx only.

Duplicate the even-indexed lanes to the odd lanes.

let a = m256::from_array([1.0, 12.0, -1.0, 3.0, 0.0, 7.0, 2.0, 50.0]);
let c = duplicate_even_lanes_m256(a).to_array();
assert_eq!(c, [12.0, 12.0, 3.0, 3.0, 7.0, 7.0, 50.0, 50.0]);