FinalityEngine in substrate relay (#1374)

* introduce FinalityEngine in relay code

* add FinalityEngine to relay

* spelling

* fix test compilation

* Update relays/lib-substrate-relay/src/finality/source.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

Co-authored-by: Adrian Catangiu <adrian@parity.io>

bridges/relays/client-substrate/src/client.rs

@@ -704,8 +704,8 @@ impl<C: Chain> Client<C> {
 		.await
 	}
 
-	/// Return new justifications stream.
-	pub async fn subscribe_justifications(&self) -> Result<Subscription<Bytes>> {
+	/// Return new GRANDPA justifications stream.
+	pub async fn subscribe_grandpa_justifications(&self) -> Result<Subscription<Bytes>> {
 		let subscription = self
 			.jsonrpsee_execute(move |client| async move {
 				Ok(client

bridges/relays/client-substrate/src/error.rs

@@ -45,9 +45,9 @@ pub enum Error {
 	/// Account does not exist on the chain.
 	#[error("Account does not exist on the chain.")]
 	AccountDoesNotExist,
-	/// Runtime storage is missing mandatory ":code:" entry.
-	#[error("Mandatory :code: entry is missing from runtime storage.")]
-	MissingMandatoryCodeEntry,
+	/// Runtime storage is missing some mandatory value.
+	#[error("Mandatory storage value is missing from the runtime storage.")]
+	MissingMandatoryStorageValue,
 	/// The client we're connected to is not synced, so we can't rely on its state.
 	#[error("Substrate client is not synced {0}.")]
 	ClientNotSynced(Health),

bridges/relays/client-substrate/src/metrics/storage_proof_overhead.rs

@@ -72,7 +72,7 @@ impl<C: Chain> StorageProofOverheadMetric<C> {
 		let maybe_encoded_storage_value =
 			storage_value_reader.read_value(CODE).map_err(Error::StorageProofError)?;
 		let encoded_storage_value_size =
-			maybe_encoded_storage_value.ok_or(Error::MissingMandatoryCodeEntry)?.len();
+			maybe_encoded_storage_value.ok_or(Error::MissingMandatoryStorageValue)?.len();
 
 		Ok(storage_proof_size - encoded_storage_value_size)
 	}