Add use std::arch::aarch64::*; to simd.rs to compile on Mac M1 with simd feature enabled

[apps4uco]

There are 11 compile errors on master when building on a Mac m1 with simd feature enabled.

This is fixed by adding

#[cfg(any(target_arch = "aarch64", target_arch = "arm"))]
use std::arch::aarch64::*;

to simd.rs.

All tests pass

cargo test -F simd

Please let me know if you need anything else in order to merge this PR.

[apps4uco]

Ive just seen that the function _mm_movemask_epi8 in simd.rs is duplicated in node16.rs so Im not sure if you were in the middle of a refactoring, in any case its compiling on Mac now. Thanks