Refactor message relay helpers (#1234)

* refactor message relay helpers

* single standalone_metrics function

* fixed tests

* clippy + fmt

* removed commented code

* add calls tracing

* fix spelling

* cargo fmt

* -commented code

* fix build again

* post-merge build fix

* clippy + fmt

bridges/modules/grandpa/src/mock.rs

@@ -106,6 +106,13 @@ impl Chain for TestBridgedChain {
 	type Balance = u64;
 	type Index = u64;
 	type Signature = Signature;
+
+	fn max_extrinsic_size() -> u32 {
+		unreachable!()
+	}
+	fn max_extrinsic_weight() -> Weight {
+		unreachable!()
+	}
 }
 
 pub fn run_test<T>(test: impl FnOnce() -> T) -> T {