Set clippy lints in workspace (requires rust 1.74) (#2390)

We currently use a bit of a hack in `.cargo/config` to make sure that
clippy isn't too annoying by specifying the list of lints.

There is now a stable way to define lints for a workspace. The only down
side is that every crate seems to have to opt into this so there's a
*few* files modified in this PR.

Dependencies:

- [x] PR that upgrades CI to use rust 1.74 is merged.

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Branislav Kontur <bkontur@gmail.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>

polkadot/node/core/pvf/benches/host_prepare_rococo_runtime.rs

@@ -28,7 +28,8 @@ use tokio::{runtime::Handle, sync::Mutex};
 const TEST_PREPARATION_TIMEOUT: Duration = Duration::from_secs(30);
 
 struct TestHost {
-	// Keep a reference to the tempdir as it gets deleted on drop.
+	// Keep a reference to the tempdir otherwise it gets deleted on drop.
+	#[allow(dead_code)]
 	cache_dir: tempfile::TempDir,
 	host: Mutex<ValidationHost>,
 }