PVF preparation: do not conflate errors (#6384)

* PVF preparation: do not conflate errors

+ Adds some more granularity to the prepare errors.
+ Better distinguish whether errors occur on the host side or the worker.
+ Do not kill the worker if the error happened on the host side.
+ Do not retry preparation if the error was `Panic`.
+ Removes unnecessary indirection with `Selected` type.

* Add missing docs, resolve TODOs

* Address review comments and remove TODOs

* Fix error in CI

* Undo unnecessary change

* Update couple of comments

* Don't return error for stream shutdown

* Update node/core/pvf/src/worker_common.rs

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

@@ -776,16 +776,15 @@ fn can_retry_prepare_after_failure(
 	num_failures: u32,
 	error: &PrepareError,
 ) -> bool {
-	use PrepareError::*;
-	match error {
-		// Gracefully returned an error, so it will probably be reproducible. Don't retry.
-		Prevalidation(_) | Preparation(_) => false,
-		// Retry if the retry cooldown has elapsed and if we have already retried less than
-		// `NUM_PREPARE_RETRIES` times. IO errors may resolve themselves.
-		Panic(_) | TimedOut | DidNotMakeIt =>
-			SystemTime::now() >= last_time_failed + PREPARE_FAILURE_COOLDOWN &&
-				num_failures <= NUM_PREPARE_RETRIES,
+	if error.is_deterministic() {
+		// This error is considered deterministic, so it will probably be reproducible. Don't retry.
+		return false
 	}
+
+	// Retry if the retry cooldown has elapsed and if we have already retried less than `NUM_PREPARE_RETRIES` times. IO
+	// errors may resolve themselves.
+	SystemTime::now() >= last_time_failed + PREPARE_FAILURE_COOLDOWN &&
+		num_failures <= NUM_PREPARE_RETRIES
 }
 
 /// A stream that yields a pulse continuously at a given interval.