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/cli/src/service.rs

@@ -401,9 +401,9 @@ mod tests {
 			let babe_pre_digest = loop {
 				inherent_data.replace_data(timestamp::INHERENT_IDENTIFIER, &(slot_num * SLOT_DURATION));
 				if let Some(babe_pre_digest) = babe::test_helpers::claim_slot(
-					&*service.client(),
-					&parent_id,
 					slot_num,
+					&parent_header,
+					&*service.client(),
 					(278, 1000),
 					&keystore,
 				) {