Remove decoding bit from "extrinsics" and reference decoding in "blocks" (#951)

* Remove decoding bits from 'tx' and reference decoding in 'blocks' instead

* newline

* doc and fmt fixes

examples/examples/blocks_subscribing.rs

@@ -31,8 +31,12 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             let events = ext.events().await?;
             let bytes_hex = format!("0x{}", hex::encode(ext.bytes()));
 
+            // See the API docs for more ways to decode extrinsics:
+            let decoded_ext = ext.as_root_extrinsic::<polkadot::Call>();
+
             println!("    Extrinsic #{idx}:");
             println!("      Bytes: {bytes_hex}");
+            println!("      Decoded: {decoded_ext:?}");
             println!("      Events:");
 
             for evt in events.iter() {