Function hash_multithreaded_with 

pub fn hash_multithreaded_with(mode: Mode<'_>, input: &[u8]) -> Hash

hash_multithreaded in any Mode, at its speed.

use blake3_servil::Mode;
let key = [7u8; 32];
let input = vec![1u8; 1 << 20];
assert_eq!(blake3_servil::hash_multithreaded_with(Mode::Keyed(&key), &input), blake3_servil::hash_with(Mode::Keyed(&key), &input));