Split RPCs into a separate crate (#1910)

* WIP extract RPCs into separate crate

* fmt

* Fix test

* Remove unused deps

* fix import

* WIP: Fix up errors and most tests. Start extracintg some tests/code to rpc crate

* MockRpcClient sync or async

* MockRpcClient only async but better type inference

* WIP MockRpcClient FnMuts and some test updates to use it

* Get all but one test working with new MockRpcClient

* WIP trying to debug failure

* WIP, Tests mostly fixed, need to add back oen more

* Get mock RPC tests working

* fmt

* fmt

* Clippy and comment tweak

* update CI to explicitly check subxt-rpc features

* clippy

* small tweaks after pass over

* feature flag rename

* update some docs

* Fix some examples

* fmt

* Fix features flags to work with web/wasm32

* Fix unused dep warning

* explicit targets in wasm CI

* Add better crate level docs

* fmt

* Address review comments

* Comment out flaky test for now and make more obvious how similar POlkadot and Substrate configs are

* Not a doc comment

* Remove unused imports

subxt/src/backend/chain_head/follow_stream_unpin.rs

@@ -4,12 +4,12 @@
 
 use super::follow_stream::FollowStream;
 use super::ChainHeadRpcMethods;
-use crate::backend::chain_head::rpc_methods::{
-    BestBlockChanged, Finalized, FollowEvent, Initialized, NewBlock,
-};
 use crate::config::{BlockHash, Config};
 use crate::error::Error;
 use futures::stream::{FuturesUnordered, Stream, StreamExt};
+use subxt_rpcs::methods::chain_head::{
+    BestBlockChanged, Finalized, FollowEvent, Initialized, NewBlock,
+};
 
 use std::collections::{HashMap, HashSet};
 use std::future::Future;