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/primitives/test-helpers/src/lib.rs

@@ -70,9 +70,9 @@ pub fn dummy_candidate_receipt_bad_sig(
 pub fn dummy_candidate_commitments(head_data: impl Into<Option<HeadData>>) -> CandidateCommitments {
 	CandidateCommitments {
 		head_data: head_data.into().unwrap_or(dummy_head_data()),
-		upward_messages: vec![],
+		upward_messages: vec![].try_into().expect("empty vec fits within bounds"),
 		new_validation_code: None,
-		horizontal_messages: vec![],
+		horizontal_messages: vec![].try_into().expect("empty vec fits within bounds"),
 		processed_downward_messages: 0,
 		hrmp_watermark: 0_u32,
 	}