chore: use new stable avx512 types from rust 1.89

[nsarlin-zama]

With the release of rust 1.89, stdarch_x86_avx512 has been stabilized and do not need the use of a nightly toolchain.
This PR adds support for these types in the avx512_simd feature.

The nightly_stdsimd feature has been kept for backward compatibility but I can remove it if you prefer.

[zachs18]

These should also use all(.., any(..)), like in zeroable.rs, not just all(..)

[Lokathor]

They should also stop requiring the nightly feature, just the avx512_simd feature.

[nsarlin-zama]

These should also use all(.., any(..)), like in zeroable.rs, not just all(..)

Yes indeed! I went a bit too fast on that one.

They should also stop requiring the nightly feature, just the avx512_simd feature.

Ok! I removed it in the last commit

[Lokathor]

My first instinct is to remove the nightly feature, but there always might be more nightly types, so it can sit doing nothing for a while. Probably better to keep churn low.

[nsarlin-zama]

My first instinct is to remove the nightly feature, but there always might be more nightly types, so it can sit doing nothing for a while. Probably better to keep churn low.

Makes sense, for example the avx512 fp16 types are still nightly gated (but not supported by bytemuck at the moment).