Support V16 metadata and refactor metadata code (#1967)

* WIP integrate unstable v16 metadata into Subxt

* first pass moving retain to the CLI tool

* Remove otuer enum variant stripping and move now simpler strip_metadata to new crate. test it

* tidyup to use stripmetadata package etc

* Fix / comment out tests

* fmt

* clippy

* Fix wasm example

* wasm-example fix

* wasm-example fix

* Maske sure to move IDs around after types.retain()

* fmt

* Tweak comment

* Find dispatch error separately to avoid issues during mapping

* Expose associated type information in pallet metadata

* Hopefully fix flaky archive RPC

* remove unwanted temp file

* Address nits

* Add back commented-otu tests and address review comments

* use either, and simplify for_each

examples/wasm-example/src/services.rs

@@ -140,8 +140,8 @@ pub async fn extension_signature_for_extrinsic(
     let signed_extensions: Vec<String> = api
         .metadata()
         .extrinsic()
-        .transaction_extensions()
-        .iter()
+        .transaction_extensions_by_version(0)
+        .unwrap()
         .map(|e| e.identifier().to_string())
         .collect();
     let tip = encode_then_hex(&Compact(0u128));