Add SSE41 path for streamvbyte_compressedbytes.

[ishitatsuyuki]

I'm trying to use compressedbytes to get the allocation size beforehand but this turned out to be awfully slow and taking more time than just doing the (SIMD-accelerated) encoding itself.

This PR fixes that and does a few things:

• It makes scalar compressedbytes branchless so that it's less awful.
• It adds a SSE41 path for compressedbytes, reusing mask calculation from the encode path.
  • Sorry, but there is no implementation for:
  • ARM NEON (don't have a machine to test)
  • 0124 path (don't have unit tests and the code structure is somewhat different).

[lemire]

This will be part of the next release.

[lemire]

I'll merge as soon as the tests are green.

[ishitatsuyuki]

Fixed the pragma errors from CI.

[lemire]

Let us re-run the tests.

[lemire]

Merging.