VRF refactory (#13889)

* First iteration to encapsulate schnorrkel and merlin usage

* Remove schnorkel direct dependency from BABE pallet

* Remove schnorrkel direct dependency from BABE client

* Trivial renaming for VrfTranscript data and value

* Better errors

* Expose a function to get a schnorrkel friendly transcript

* Keep the vrf signature stuff together (preventing some clones around)

* Fix tests

* Remove vrf agnostic transcript and define it as an associated type for VrfSigner and VrfVerifier

* Fix babe pallet mock

* Inner types are required to be public for polkadot

* Update client/consensus/babe/src/verification.rs

Co-authored-by: Koute <koute@users.noreply.github.com>

* Nit

* Remove Deref implementations

* make_bytes as a method

* Trigger CI

---------

Co-authored-by: Koute <koute@users.noreply.github.com>

substrate/client/consensus/babe/src/migration.rs

@@ -18,7 +18,7 @@
 
 use crate::{
 	AuthorityId, BabeAuthorityWeight, BabeConfiguration, BabeEpochConfiguration, Epoch,
-	NextEpochDescriptor, VRF_OUTPUT_LENGTH,
+	NextEpochDescriptor, Randomness,
 };
 use codec::{Decode, Encode};
 use sc_consensus_epochs::Epoch as EpochT;
@@ -36,7 +36,7 @@ pub struct EpochV0 {
 	/// The authorities and their weights.
 	pub authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
 	/// Randomness for this epoch.
-	pub randomness: [u8; VRF_OUTPUT_LENGTH],
+	pub randomness: Randomness,
 }
 
 impl EpochT for EpochV0 {