chainHead: Add support for storage closest merkle descendant #14818 (#1153)

This PR adds support for fetching the closest merkle value of some key.


Builds on top of
- https://github.com/paritytech/trie/pull/199

Migrates https://github.com/paritytech/substrate/pull/14818 to the
monorepo.
Closes: https://github.com/paritytech/substrate/issues/14550
Closes: https://github.com/paritytech/polkadot-sdk/issues/1506

// @paritytech/subxt-team

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

substrate/client/rpc-spec-v2/src/chain_head/test_utils.rs

@@ -20,8 +20,8 @@ use parking_lot::Mutex;
 use sc_client_api::{
 	execution_extensions::ExecutionExtensions, BlockBackend, BlockImportNotification,
 	BlockchainEvents, CallExecutor, ChildInfo, ExecutorProvider, FinalityNotification,
-	FinalityNotifications, FinalizeSummary, ImportNotifications, KeysIter, PairsIter, StorageData,
-	StorageEventStream, StorageKey, StorageProvider,
+	FinalityNotifications, FinalizeSummary, ImportNotifications, KeysIter, MerkleValue, PairsIter,
+	StorageData, StorageEventStream, StorageKey, StorageProvider,
 };
 use sc_utils::mpsc::{tracing_unbounded, TracingUnboundedSender};
 use sp_api::{CallApiAt, CallApiAtParams, NumberFor, RuntimeVersion};
@@ -198,6 +198,23 @@ impl<
 	) -> sp_blockchain::Result<Option<Block::Hash>> {
 		self.client.child_storage_hash(hash, child_info, key)
 	}
+
+	fn closest_merkle_value(
+		&self,
+		hash: Block::Hash,
+		key: &StorageKey,
+	) -> sp_blockchain::Result<Option<MerkleValue<Block::Hash>>> {
+		self.client.closest_merkle_value(hash, key)
+	}
+
+	fn child_closest_merkle_value(
+		&self,
+		hash: Block::Hash,
+		child_info: &ChildInfo,
+		key: &StorageKey,
+	) -> sp_blockchain::Result<Option<MerkleValue<Block::Hash>>> {
+		self.client.child_closest_merkle_value(hash, child_info, key)
+	}
 }
 
 impl<Block: BlockT, Client: CallApiAt<Block>> CallApiAt<Block> for ChainHeadMockClient<Client> {