Use frame-decode for core extrinsic decode logic (#1785)

* WIP using frame-decode for core extrinsic decode logic

* fmt

* Fix dependabot config

* clippy

* tidy some imports

* Fix a couple of tests

* Update to frame-decode 0.0.7

* fix docs

* Decode exts earlier to avoid doing it every iter/find step

* frame-decode to 0.1.0

* fmt

* clippy

* fix wasm example

* doc test fixes

* Fix test

* Fix a couple of subxt_core tests

subxt/examples/block_decoding_dynamic.rs

@@ -17,8 +17,6 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         // Decode each signed extrinsic in the block dynamically
         let extrinsics = block.extrinsics().await?;
         for ext in extrinsics.iter() {
-            let ext = ext?;
-
             let Some(signed_extensions) = ext.signed_extensions() else {
                 continue; // we do not look at inherents in this example
             };
@@ -29,7 +27,6 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             println!("  {}/{}", meta.pallet.name(), meta.variant.name);
             println!("    Signed Extensions:");
             for signed_ext in signed_extensions.iter() {
-                let signed_ext = signed_ext?;
                 // We only want to take a look at these 3 signed extensions, because the others all just have unit fields.
                 if ["CheckMortality", "CheckNonce", "ChargeTransactionPayment"]
                     .contains(&signed_ext.name())