Add workflow for clippy

[vks]

No description provided.

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[dhardy]

Clippy still only half convinces me of its utility, but since this project is relatively stable and this Action only uses the stable version, this addition seems reasonable.

[dhardy]

If I understand correctly, this will check the rand and rand_core (a dependency), but not other crates.

Maybe use --all (but then --all-features does not apply correctly to other crates) or --no-deps and check each crate separately.

[vks]

It seems there are a bunch of deprecation warnings... ☹️

This is a bit frustrating, since this is the file that GitHub currently suggests... 😅

[newpavlov]

In my experience it's better to use a fixed toolchain version for a Clippy job and bump it from time to time manually. Otherwise, on new stable release we may get unrelated CI failures in PRs.