refactor(web): redo proof of work web worker logic (#941)

* chore(web/js): delete proof-of-work-slow.mjs

This code has served its purpose and now needs to be retired to the
great beyond. There is no replacement for this, the fast implementation
will be used instead.

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

* chore(web): handle building multiple JS entrypoints and web workers

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

* feat(web): rewrite frontend worker handling

This completely rewrites how the proof of work challenge works based on
feedback from browser engine developers and starts the process of making
the proof of work function easier to change out.

- Import @aws-crypto/sha256-js to use in Firefox as its implementation
  of WebCrypto doesn't jump directly from highly optimized browser
  internals to JIT-ed JavaScript like Chrome's seems to.
- Move the worker code to `web/js/worker/*` with each worker named after
  the hashing method and hash method implementation it uses.
- Update bench.mjs to import algorithms the new way.
- Delete video.mjs, it was part of a legacy experiment that I never had
  time to finish.
- Update LibreJS comment to add info about the use of
  @aws-crypto/sha256-js.
- Also update my email to my @techaro.lol address.

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

* fix(web): don't hard dep webcrypto anymore

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

* chore(lib/policy): start the deprecation process for slow

This mostly adds a warning, but the "slow" method is in the process of
being removed. Warn admins with slog.Warn.

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

* docs: update CHANGELOG

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

* feat(web/js): allow running Anubis in non-secure contexts

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

* Update metadata

check-spelling run (pull_request) for Xe/purge-slow

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on-behalf-of: @check-spelling <check-spelling-bot@check-spelling.dev>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>
Signed-off-by: check-spelling-bot <check-spelling-bot@users.noreply.github.com>

docs/docs/CHANGELOG.md

@@ -19,6 +19,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - The [`segments`](./admin/configuration/expressions.mdx#segments) function was added for splitting a path into its slash-separated segments.
 - When issuing a challenge, Anubis stores information about that challenge into the store. That stored information is later used to validate challenge responses. This works around nondeterminism in bot rules. ([#917](https://github.com/TecharoHQ/anubis/issues/917))
 - When parsing [Open Graph tags](./admin/configuration/open-graph.mdx), add any URLs found in the responses to a temporary "allow cache" so that social preview images work.
+- Proof of work solving has had a complete overhaul and rethink based on feedback from browser engine developers, frontend experts, and overall performance profiling.
+- One of the biggest sources of lag in Firefox has been eliminated: the use of WebCrypto. Now whenever Anubis detects the client is using Firefox (or Pale Moon), it will swap over to a pure-JS implementation of SHA-256 for speed.
+- Web Workers are stored as dedicated JavaScript files in `static/js/workers/*.mjs`.
+- Pave the way for non-SHA256 solver methods and eventually one that uses WebAssembly (or WebAssembly code compiled to JS for those that disable WebAssembly).
+- Legacy JavaScript code has been eliminated.
+- The contact email in the LibreJS header has been changed.
+- The hard dependency on WebCrypto has been removed, allowing a proof of work challenge to work over plain (unencrypted) HTTP.
+
+### Breaking changes
+
+- The "slow" frontend solver has been removed in order to reduce maintenance burden. Any existing uses of it will still work, but issue a warning upon startup asking administrators to upgrade to the "fast" frontend solver.
 
 ## v1.21.3: Minfilia Warde - Echo 3