Use CPU clock timeout for PVF jobs (#6282)

* Put in skeleton logic for CPU-time-preparation

Still needed:
- Flesh out logic
- Refactor some spots
- Tests

* Continue filling in logic for prepare worker CPU time changes

* Fix compiler errors

* Update lenience factor

* Fix some clippy lints for PVF module

* Fix compilation errors

* Address some review comments

* Add logging

* Add another log

* Address some review comments; change Mutex to AtomicBool

* Refactor handling response bytes

* Add CPU clock timeout logic for execute jobs

* Properly handle AtomicBool flag

* Use `Ordering::Relaxed`

* Refactor thread coordination logic

* Fix bug

* Add some timing information to execute tests

* Add section about the mitigation to the IG

* minor: Change more `Ordering`s to `Relaxed`

* candidate-validation: Fix build errors

polkadot/node/core/pvf/src/artifacts.rs

@@ -101,6 +101,8 @@ pub enum ArtifactState {
 		/// This is updated when we get the heads up for this artifact or when we just discover
 		/// this file.
 		last_time_needed: SystemTime,
+		/// The CPU time that was taken preparing this artifact.
+		cpu_time_elapsed: Duration,
 	},
 	/// A task to prepare this artifact is scheduled.
 	Preparing {
@@ -171,11 +173,16 @@ impl Artifacts {
 	/// This function must be used only for brand-new artifacts and should never be used for
 	/// replacing existing ones.
 	#[cfg(test)]
-	pub fn insert_prepared(&mut self, artifact_id: ArtifactId, last_time_needed: SystemTime) {
+	pub fn insert_prepared(
+		&mut self,
+		artifact_id: ArtifactId,
+		last_time_needed: SystemTime,
+		cpu_time_elapsed: Duration,
+	) {
 		// See the precondition.
 		always!(self
 			.artifacts
-			.insert(artifact_id, ArtifactState::Prepared { last_time_needed })
+			.insert(artifact_id, ArtifactState::Prepared { last_time_needed, cpu_time_elapsed })
 			.is_none());
 	}