refactor to standard library portable_simd feature

[KonradHoeffner]

As packed_simd no longer works with Rust nightly 1.78 (see rust-lang/packed_simd#359), this PR tries to refactor to the nightly-only portable_simd feature.

Warning I am not a SIMD expert and while it builds, some tests still fail, however I cannot find the reason right now.
I also used transmute, so this should go through a thorough review.

[KonradHoeffner]

@sujayakar: Could you take a look into this PR? If this got merged this could help resolve several open issues in other projects.

[sujayakar]

hey @KonradHoeffner, sorry for the delay getting back to you. I don't currently have an x64 machine for work anymore, so I had to get a dev setup up and running on my gaming PC (AMD Zen2).

the PR overall looks good, and I wasn't getting any test failures when I patched it in locally. In particular, I did

$ QUICKCHECK_TESTS=10000 cargo test --release --features simd qc_rsdict

and the tests passed. what failures are you running into?

[Cydhra]

The failures have been fixed by ee11266

[KonradHoeffner]

@sujayakar Thanks for looking into this! I've recently refactored our library to use sucds instead but I'm sure this will be helpful for a lot of other users. Yes, @Cydhra fixed all the errors.

[sujayakar]

thanks for the fixes! I'll do a crates.io release shortly.