Small micro-optimizations for Sha1

[Squareys]

Hi @mosra,

as mentioned on gitter, here's the minor optimizations I did. The only really significant one is 3b0bce3352455e095bca9b2130dd0c5fada4472d, in case you want to cherry-pick it for minimal invasiveness.

Best, Jonathan

[mosra]

(Argh, May last year and still not merged? What am I doing.)

Just FYI, I'm going to need fast hashing for image deduplication and so will get back to this soon. And with the Cpu library now being a thing and my new laptop implementing the x86 SHA instructions I'll be looking into making a proper implementation with competitive perf ;)

[Squareys]

No worries, we have since switched to xxhash3, which has insanely high throughput.