Support x86 AVX-12 SIMD types on 1.89.0 stable

[joshlf]

Previously, these types were gated by the stdarch_x86_avx512 nightly
Rust feature. As of 1.89.0, they are supported on stable.

Closes #2583

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This PR is on branch simd-x86-avx12.

• Support x86 AVX-12 SIMD types on 1.89.0 stable #2574

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.75%. Comparing base (0e51bab) to head (ca6c178).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2574   +/-   ##
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  Coverage   88.75%   88.75%           
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  Files          20       20           
  Lines        5343     5343           
=======================================
  Hits         4742     4742           
  Misses        601      601           

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[jswrenn]

I think we should punt on this until 1.89 is released, and in the meantime -A stable_features in our nightly CI runs. That will allow us to get the nightly CI roller working again.

[joshlf]

Blocked on #2583.

[usamoi]

In these four types __m512bh, __m512, __m512d, and __m512i, only __m512bh was stabilized in Rust 1.89, while the other three were stabilized in Rust 1.72. Does it make sense to lower the required Rust version to 1.72?

See also: rust-lang/stdarch#1436