Change storage key arguments (and call arguments?) to being references

[jsdw]

Currently we pass these by value:

84fe1a0

But we can see in an example of the generated code that we only need a reference ultimately:

pub async fn pending_swap(
    &self,
    _0: runtime_types::polkadot_parachain::primitives::Id,
    hash: ::core::option::Option<T::Hash>,
) -> ::core::result::Result<
    ::core::option::Option<
        runtime_types::polkadot_parachain::primitives::Id,
    >,
    ::subxt::BasicError,
> {
    let entry = PendingSwap(_0);
    self.client.storage().fetch(&entry, hash).await
}

[ascjones]

💯 would be good to add this before we release.