Fast sync child trie support. (#9239)

* state machine proofs.

* initial implementation

* Remove todo.

* Extend test and fix import.

* fix no proof, with proof ko.

* fix start at logic.

* Restore response size.

* Rework comments.

* Add explicit ref

* Use compact proof.

* ref change

* elaborato on empty change set condition.

* KeyValueState renaming.

* Do not add two time child trie with same root to sync reply.

* rust format

* Fix merge.

* fix warnings and fmt

* fmt

* update protocol id to V2

substrate/test-utils/runtime/client/src/lib.rs

@@ -137,6 +137,11 @@ impl GenesisParameters {
 	pub fn set_wasm_code(&mut self, code: Vec<u8>) {
 		self.wasm_code = Some(code);
 	}
+
+	/// Access extra genesis storage.
+	pub fn extra_storage(&mut self) -> &mut Storage {
+		&mut self.extra_storage
+	}
 }
 
 impl substrate_test_client::GenesisInit for GenesisParameters {