The storage runtime interface should not enforce a hash type (#4231)

* The storage runtime interface should not enforce a hash type

Currently the runtime interface enforces `H256` as hash type, but in the
future people could use whatever they want as hash type. The hash type
always needs to match between the runtime and the node, but that is
already required.

* Update primitives/externalities/src/lib.rs

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

substrate/client/src/light/fetcher.rs

@@ -70,7 +70,7 @@ impl<E, H, B: BlockT, S: BlockchainStorage<B>> LightDataChecker<E, H, B, S> {
 	) -> ClientResult<Vec<(NumberFor<B>, u32)>>
 		where
 			H: Hasher,
-			H::Out: Ord,
+			H::Out: Ord + codec::Codec,
 	{
 		// since we need roots of all changes tries for the range begin..max
 		// => remote node can't use max block greater that one that we have passed
@@ -148,7 +148,7 @@ impl<E, H, B: BlockT, S: BlockchainStorage<B>> LightDataChecker<E, H, B, S> {
 	) -> ClientResult<()>
 		where
 			H: Hasher,
-			H::Out: Ord,
+			H::Out: Ord + codec::Codec,
 	{
 		// all the checks are sharing the same storage
 		let storage = create_proof_check_backend_storage(remote_roots_proof);