Use a BoundedVec in ValidationResult (#6603)

* Use a `BoundedVec` in `ValidationResult`

> Use a `BoundedVec` for `upward_messages` and `horizontal_messages` in order to
> limit the number of individual messages/memory allocations right at decoding
> time. The reason for this is that the `ValidationResult` may contain a code
> upgrade (including a full PVF binary), so the total size limit can't be set
> too low and this limit will still allow several millions of upward messages,
> which will (due to the memory allocator overhead) already have a
> non-negligible memory footprint in decoded form.

* List all fields when hashing so we don't miss one

* Define types for  `BoundedVec`s of messages

* Fix test compile errors

* Depend on `bounded-collections` 0.1.4 (fixes allocation issue)

* Fix compilation issue

* Derive `Hash` instead of manual `impl`

* Avoid use of unwrap

polkadot/node/malus/src/variants/common.rs

@@ -163,8 +163,8 @@ pub fn create_fake_candidate_commitments(
 	persisted_validation_data: &PersistedValidationData,
 ) -> CandidateCommitments {
 	CandidateCommitments {
-		upward_messages: Vec::new(),
-		horizontal_messages: Vec::new(),
+		upward_messages: Default::default(),
+		horizontal_messages: Default::default(),
 		new_validation_code: None,
 		head_data: persisted_validation_data.parent_head.clone(),
 		processed_downward_messages: 0,