hilbert: implement zorder for archs other than x86_64

[hhirtz]

• for x86: use twice as many pdep32s and OR the results,
• for other archs: loop over the bits. I didn't measure the performance.

Don't need this for now, and fallback code compiles to a lot of instructions, so I'll keep this PR open

Fixes #260

TODO

• [ ] unit tests

[codecov[bot]]

Codecov Report

Base: 55.47% // Head: 56.04% // Increases project coverage by +0.57% :tada:

Coverage data is based on head (ef30337) compared to base (7461d81). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #273 +/- ## ========================================== + Coverage 55.47% 56.04% +0.57% ========================================== Files 41 41 Lines 7530 7565 +35 ========================================== + Hits 4177 4240 +63 + Misses 3353 3325 -28 ``` | [Impacted Files](https://codecov.io/gh/LIHPC-Computational-Geometry/coupe/pull/273?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LIHPC-Computational-Geometry) | Coverage Δ | | |---|---|---| | [src/algorithms/hilbert\_curve.rs](https://codecov.io/gh/LIHPC-Computational-Geometry/coupe/pull/273/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LIHPC-Computational-Geometry#diff-c3JjL2FsZ29yaXRobXMvaGlsYmVydF9jdXJ2ZS5ycw==) | `85.92% <100.00%> (+0.96%)` | :arrow_up: | | [src/algorithms/vn/first.rs](https://codecov.io/gh/LIHPC-Computational-Geometry/coupe/pull/273/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LIHPC-Computational-Geometry#diff-c3JjL2FsZ29yaXRobXMvdm4vZmlyc3QucnM=) | `91.22% <0.00%> (+0.87%)` | :arrow_up: | | [src/algorithms/arc\_swap.rs](https://codecov.io/gh/LIHPC-Computational-Geometry/coupe/pull/273/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LIHPC-Computational-Geometry#diff-c3JjL2FsZ29yaXRobXMvYXJjX3N3YXAucnM=) | `84.70% <0.00%> (+10.07%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LIHPC-Computational-Geometry). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LIHPC-Computational-Geometry)

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[cedricchevalier19]

Related to #310

[cedricchevalier19]

Already done in #310