Distinct handling for N fields + 1 hasher vs N fields + N hashers (#458)

* Distinct handling for N fields + 1 hasher vs N fields + N hashers

* tweak comment

* cargo fmt

* fix typo

* Add a few storage specific tests

* clippy fixes

* cargo fmt

* Add a test to specifically address this fix

* comment typo

* Address niggles

* slgihtly nicer iter code

subxt/tests/integration/main.rs

@@ -23,6 +23,8 @@ mod client;
 mod events;
 #[cfg(test)]
 mod frame;
+#[cfg(test)]
+mod storage;
 
 use test_runtime::node_runtime;
 use utils::*;