Batch transactions in complex relays (#1669)

* batch transactions in message relay: API prototype

* get rid of Box<dyn BatchTransaction> and actually submit it

* test batch transactions

* message_lane_loop_works_with_batch_transactions

* removed logger

* BatchConfirmationTransaction + BatchDeliveryTransaction

* more prototyping

* fmt

* continue with batch calls

* impl BatchCallBuilder for ()

* BatchDeliveryTransaction impl

* BundledBatchCallBuilder

* proper impl of BundledBatchCallBuilder + use it in RialtoParachain -> Millau

* impl prove_header in OnDemandHeadersRelay

* impl OnDemandParachainsRelay::prove_header (needs extensive tests)

* added a couple of TODOs

* return Result<Option<BatchTx>> when asking for more headers

* prove headers when reauire_* is called && return proper headers from required_header_id

* split parachains::prove_header and test select_headers_to_prove

* more traces and leave TODOs

* use finality stream in SubstrateFinalitySource::prove_block_finality

* prove parachain head at block, selected by headers relay

* const ANCIENT_BLOCK_THRESHOLD

* TODO -> proof

* clippy and spelling

* BatchCallBuilder::build_batch_call() returns Result

* read first proof from two streams

* FailedToFindFinalityProof -> FinalityProofNotFound

* changed select_headers_to_prove to version from PR review

bridges/relays/messages/src/message_race_receiving.rs

@@ -155,9 +155,13 @@ where
 {
 	type Error = C::Error;
 	type TargetNoncesData = ();
+	type BatchTransaction = C::BatchTransaction;
 	type TransactionTracker = C::TransactionTracker;
 
-	async fn require_source_header(&self, id: TargetHeaderIdOf<P>) {
+	async fn require_source_header(
+		&self,
+		id: TargetHeaderIdOf<P>,
+	) -> Result<Option<C::BatchTransaction>, Self::Error> {
 		self.client.require_target_header_on_source(id).await
 	}