Add ABI crate

Call and Event are both from the pallets, which are AGPL licensed. Accordingly,
they make serai-client AGPL licensed when serai-client must end up MIT
licensed. This creates a MIT-licensed variant of Calls and Events such that
they can be used by serai-client, enabling transitioning it to MIT.

Relevant to https://github.com/serai-dex/serai/issues/337.

substrate/abi/src/validator_sets.rs

@@ -0,0 +1,68 @@
+pub use serai_validator_sets_primitives as primitives;
+
+use serai_primitives::*;
+use serai_validator_sets_primitives::*;
+
+#[derive(Clone, PartialEq, Eq, Debug, scale::Encode, scale::Decode)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+pub enum Call {
+  set_keys {
+    network: NetworkId,
+    key_pair: KeyPair,
+    signature: Signature,
+  },
+  remove_participant {
+    network: NetworkId,
+    to_remove: SeraiAddress,
+    signers: Vec<SeraiAddress>,
+    signature: Signature,
+  },
+  allocate {
+    network: NetworkId,
+    amount: Amount,
+  },
+  deallocate {
+    network: NetworkId,
+    amount: Amount,
+  },
+  claim_deallocation {
+    network: NetworkId,
+    session: Session,
+  },
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, scale::Encode, scale::Decode)]
+#[cfg_attr(feature = "borsh", derive(borsh::BorshSerialize, borsh::BorshDeserialize))]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+pub enum Event {
+  NewSet {
+    set: ValidatorSet,
+  },
+  ParticipantRemoved {
+    set: ValidatorSet,
+    removed: SeraiAddress,
+  },
+  KeyGen {
+    set: ValidatorSet,
+    key_pair: KeyPair,
+  },
+  AllocationIncreased {
+    validator: SeraiAddress,
+    network: NetworkId,
+    amount: Amount,
+  },
+  AllocationDecreased {
+    validator: SeraiAddress,
+    network: NetworkId,
+    amount: Amount,
+    delayed_until: Option<Session>,
+  },
+  DeallocationClaimed {
+    validator: SeraiAddress,
+    network: NetworkId,
+    session: Session,
+  },
+  SetRetired {
+    set: ValidatorSet,
+  },
+}