Bandersnatch VRF (#14412)

* Introduce bandersnatch vrf

* Some documentation

* Fix tests

* Fix docs refs

* Some more docs

* Comments about key derivation

* Make clippy happy

* Fix ring context enc/dec test

* Fix docs

* Switch to upstream ring-vrf

* Use sub-domains to construct VrfInput

* Bandersnatch VRF experimental feature

* Restore upstream dep

* Fix feature flags

* Apply typo fix

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Bump bandersnatch-vrfs

* Weiestrass form has been selected

* Rename bandersnatch testing app crypto id

* Support for seed recovery

* Clarified domain size <-> key size relationship

* cargo fmt

* Trigger CI

* Some required tweaks to crypto types

* Remove leftovers from Cargo.toml

* Remove some TODO notes

* Simplification of structs construction

* Trigger CI

* Apply review suggestion

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

* Docs typo

* Fix keystore tests

* Consistence

* Add ref to git rependency

* Static check of MAX_VRF_IOS value

* Clarify behavior for out of ring keys signatures

* Add test for ring-vrf to the keystore

* Fix docs

---------

Co-authored-by: Anton <anton.kalyaev@gmail.com>
Co-authored-by: Koute <koute@users.noreply.github.com>

substrate/primitives/keyring/src/lib.rs

@@ -23,11 +23,17 @@ pub mod sr25519;
 /// Test account crypto for ed25519.
 pub mod ed25519;
 
+/// Test account crypto for bandersnatch.
+#[cfg(feature = "bandersnatch-experimental")]
+pub mod bandersnatch;
+
 /// Convenience export: Sr25519's Keyring is exposed as `AccountKeyring`,
 /// since it tends to be used for accounts (although it may also be used
 /// by authorities).
 pub use sr25519::Keyring as AccountKeyring;
 
+#[cfg(feature = "bandersnatch-experimental")]
+pub use bandersnatch::Keyring as BandersnatchKeyring;
 pub use ed25519::Keyring as Ed25519Keyring;
 pub use sr25519::Keyring as Sr25519Keyring;