Re-enable clippy in CI for stable once clap issues addressed.

[micolous]

#312 temporarily disabled Clippy in CI for 1.69 due to spuriously-failing clap correctness checks: rust-lang/rust-clippy#10421

We'll need to revert that at some point once the upstream issue is fixed in a stable release.

There's an existing request to cherry-pick the fix in rust-lang/rust-clippy#10685

[micolous]

It looks like clap 3.2.24 just disabled the correctness lints in the macros, which I think should let users explicitly disable those checks... which means we'll have a bunch of clippy allow rules for clap.

clap 4.2.x looks like it doesn't have the same issue, so migrating to that may be the easier way to address this. I've started on this in #315.