chainHead based backend implementation (#1161)

* add follow_stream impl

* follow_stream_unpin first draft

* add tests for follow_stream_unpin

* more tests and fixes for follow_stream_unpin

* first pass follow_stream_driver

* follow_stream_driver: add tests, fix things, buffer events from last finalized

* First pass finishing Backend impl

* Fix test compile issues

* clippy fixes

* clippy fix and consistify light_client

* revert lightclient tweak

* revert other lightclient thing

* cargo fmt

* start testing unstable backend behind feature flag

* more test fixes and move test-runtime metadata path just incase

* fix compile error

* ensure transaction progress stream actually used and fix another test

* cargo fmt

* CI tweak

* improve some comments and address some feedback bits

* update CI to use our own nightly binary

* wait for finalized block perhaps

testing/test-runtime/src/lib.rs

@@ -5,6 +5,9 @@
 #![allow(clippy::too_many_arguments)]
 
 /// The SCALE encoded metadata obtained from a local run of a substrate node.
-pub static METADATA: &[u8] = include_bytes!(concat!(env!("OUT_DIR"), "/metadata.scale"));
+pub static METADATA: &[u8] = include_bytes!(concat!(
+    env!("OUT_DIR"),
+    "/test_node_runtime_metadata.scale"
+));
 
 include!(concat!(env!("OUT_DIR"), "/runtime.rs"));