babe: Introduce secondary slots (Aurababeous) (#3380)

* babe: initial implementation of secondary slots

* babe: validate secondary slot author

* babe: implement weight based fork choice

* babe: remove unused

* aura: cleanup unused imports

* babe: pass in parent weight when authoring and verifying

* babe: use epoch randomness for picking secondary slot authors

* babe: fix tests

* babe: fix wasm build

* babe: node-side code for disabling secondary slots

* babe: allow enabling/disabling secondary slots from runtime

* babe: fix test

* babe: use blake2_256 for secondary slot assignment

* babe: run block initialization in should_end_session

* node: increase slot duration to 6s

* babe: add docs

* node: bump spec_version

* Apply suggestions from code review

Co-Authored-By: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* babe: simplify secondary slot assignment calculation

* babe: remove unnecessary comment

* node: bump spec_version

* babe: fix bad merge

substrate/node/runtime/src/lib.rs

@@ -80,7 +80,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// and set impl_version to equal spec_version. If only runtime
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
-	spec_version: 144,
+	spec_version: 145,
 	impl_version: 145,
 	apis: RUNTIME_API_VERSIONS,
 };
@@ -559,6 +559,7 @@ impl_runtime_apis! {
 				epoch_index: Babe::epoch_index(),
 				randomness: Babe::randomness(),
 				duration: EpochDuration::get(),
+				secondary_slots: Babe::secondary_slots().0,
 			}
 		}
 	}