ci: Pin Rust Version, don't use Nightly rustfmt features, fix Fuzz workflow

[ParkMyCar]

This PR does some cleanup:

1. Pins the version of stable Rust we use in CI to 1.83.0
2. Changes the rustfmt settings to no longer use Nightly features
   • Originally I hoped some features would be stabilized soon but alas years later they're still only available on Nightly
3. Fixes the Fuzz workflow by upgrading Rust, fixing the install of cargo-fuzz and fixes the harness