fix(js): use pure JS SHA256 library, refactor (#471)

* fix(js): use pure JS SHA256 library, refactor

Closes #458

Additionally, I made a horrifying discovery: Firefox seems to actively
hinder performance if you are using more than one Worker per page. It
does not spread the load out across cores like I expected. Instead it
seems to make that one Worker thrash and have to constantly context
switch, which caused a lot of slowdown.

The benchmarks in #155 continue to be the best contribution ever made to
Anubis. What clued me into there being a problem here was the fact that
the "slow" algorithm was faster than the "fast" algorithm on my laptop.
This made no intuitive sense to me so I dug further.

Either way I think this is a Firefox bug at its core, but for now we
have to work around it by doing the hacky terrible thing that I hate.

I also swapped the SHA256 operations to @aws-crypto/sha256-js on the
advice of a trusted cryptography expert. I don't know what performance
differences this makes, but I'm getting 150-225 kilohashes per second,
which is pretty dang good.

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(js): apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(js): use fast algo for fast worker

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

package.json

@@ -24,5 +24,8 @@
     "postcss-import": "^16.1.0",
     "postcss-import-url": "^7.2.0",
     "postcss-url": "^10.1.3"
+  },
+  "dependencies": {
+    "@aws-crypto/sha256-js": "^5.2.0"
   }
 }