Remove SIMD LaneCount, SupportedLaneCount with upstream changes

[xangelix]

Not sure exactly when this will be part of a versioned release? As such this is marked draft. This contains the required changes for SIMD compilation on the latest nightly toolchain.

See rust-lang/rust@b71ff51.

[Kerollmops]

Nice 👌 Thank you very much @xangelix for the change. Let's see where it goes.

Can you tell me if I need to land your changes to crates.io so that people can use the simd feature with the latest rustc compile, please?

[Kerollmops]

Would you mind rebasing on #349, please? It's odd because it seems to me that your PR will fix nightly, but will break the stable CI...

[xangelix]

I would be happy to rebase so your CICD can work! But to be clear, I don't think this PR breaks stable.

portable_simd is only a feature on nightly, so this comes down to which version of nightly you'd want to pin to based roughly on that linked commit above, rust-lang/rust@b71ff51 , you'd decide if you want to support before or after Jan 28th, 2026.

If you want to support nightly versions roughly after nightly-2026-01-28 then you would merge this, if you want to support roughly before nightly-2026-01-28, then you would wait on this.

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Separately about the CICD,

If you check with cargo tree:

it's tempfile which is forcing the getrandom v0.4 dependency.

Precisely v3.25.0, https://github.com/Stebalien/tempfile/blob/master/CHANGELOG.md#3250 which was released 15 days ago https://crates.io/crates/tempfile/3.25.0.

Meaning that for 15 days now, your CICD would fail even if you ran your main branch on it. (So the CICD was already broken ☹️)

Anyways, sorry for the ramble! I think this PR is just a matter of which nightly versions you might want to support. So, it's not necessary to bump the MSRV for this PR if you don't want to. Correct me if I'm wrong! 😛

Rebasing now...