Add 'Static' type and improve type substitution codegen to accept it (#886)

* Add Static type which defers to Encode/Decode and impls EncodeAsType/DecodeAsType

* rename to static_type and impl Deref/Mut

* Improve type substitution in codegen so that concrete types can be swapped in

* A couple of comment tweaks and no need for a macro export

* Extend type substitution logic to work recursively on destination type

* cargo fmt

* Fix a couple of comments

* update ui test outpuot

* Add docs and missing_docs lint

* Add test for replacing multiple of Ident

* Update codegen/src/error.rs

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

* update copyright year and fix ui test

* simplify another error

---------

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

codegen/src/utils/mod.rs

@@ -1,3 +1,9 @@
+// Copyright 2019-2023 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+//! Utilities to help with fetching and decoding metadata.
+
 mod fetch_metadata;
 
 // easy access to this type needed for fetching metadata:
@@ -5,5 +11,5 @@ pub use jsonrpsee::client_transport::ws::Uri;
 
 pub use fetch_metadata::{
     fetch_metadata_bytes, fetch_metadata_bytes_blocking, fetch_metadata_hex,
-    fetch_metadata_hex_blocking, FetchMetadataError,
+    fetch_metadata_hex_blocking,
 };