ci: Use auguwu/clippy-action@1.4.0 to run clippy

[Techcable]

Makes clippy warnings trigger warnings instead of hard errors, fixing issue #338

HACK: Use my fork of auguwu/clippy-action to support "features" input.

Split off from PR #337 , which is logically independent.

A couple issues:

The --features flag isn't working when used with check-args
We get lots of duplicate warnings by running multiple feature combinations

IDEA: Maybe run just once with --all-features?

Make sure to:

• [x] Add an entry to CHANGELOG.md (if necessary)

[Techcable]

I decided we want build failures on warnings, as discussed in #338

We only trigger build failures on warnings on the "hardcoded recent stable," so clippy changes shouldn't unexpectedly fail the build.