Remove subxt (#460)

* Remove subxt

Removes ~20 crates from our Cargo.lock.

Removes downloading the metadata and enables removing the getMetadata RPC route
(relevant to #379).

Moves forward #337.

Done now due to distinctions in the subxt 0.32 API surface which make it
justifiable to not update.

* fmt, update due to deny triggering on a yanked crate

* Correct the handling of substrate_block_notifier now that it's ephemeral, not long-lived

* Correct URL in tests/coordinator from ws to http

substrate/client/tests/common/dex.rs

@@ -20,7 +20,7 @@ pub async fn add_liquidity(
     &pair,
     &SeraiDex::add_liquidity(coin, coin_amount, sri_amount, Amount(1), Amount(1), address.into()),
     nonce,
-    Default::default(),
+    0,
   );
 
   publish_tx(serai, &tx).await