Have the coins pallet emit events via serai_core_pallet

`serai_core_pallet` solely defines an accumulator for the events. We use the
traditional `frame_system::Events` to store them for now and enable retrieval.

substrate/abi/src/coins.rs

@@ -44,6 +44,15 @@ pub enum Event {
     /// The coins minted.
     coins: Balance,
   },
+  /// The specified coins were transferred.
+  Transfer {
+    /// The address transferred from.
+    from: SeraiAddress,
+    /// The address transferred to.
+    to: SeraiAddress,
+    /// The coins transferred.
+    coins: Balance,
+  },
   /// The specified coins were burnt.
   Burn {
     /// The address burnt from.
@@ -58,13 +67,4 @@ pub enum Event {
     /// The `OutInstruction` specified, and the coins burnt.
     instruction: OutInstructionWithBalance,
   },
-  /// The specified coins were transferred.
-  Transfer {
-    /// The address transferred from.
-    from: SeraiAddress,
-    /// The address transferred to.
-    to: SeraiAddress,
-    /// The coins transferred.
-    coins: Balance,
-  },
 }

substrate/abi/src/lib.rs

@@ -96,3 +96,44 @@ pub enum Event {
   /// The event for `InInstruction`s.
   InInstructions(in_instructions::Event) = 7,
 }
+
+impl From<system::Event> for Event {
+  fn from(event: system::Event) -> Self {
+    Self::System(event)
+  }
+}
+impl From<coins::Event> for Event {
+  fn from(event: coins::Event) -> Self {
+    Self::Coins(event)
+  }
+}
+impl From<validator_sets::Event> for Event {
+  fn from(event: validator_sets::Event) -> Self {
+    Self::ValidatorSets(event)
+  }
+}
+impl From<signals::Event> for Event {
+  fn from(event: signals::Event) -> Self {
+    Self::Signals(event)
+  }
+}
+impl From<dex::Event> for Event {
+  fn from(event: dex::Event) -> Self {
+    Self::Dex(event)
+  }
+}
+impl From<genesis_liquidity::Event> for Event {
+  fn from(event: genesis_liquidity::Event) -> Self {
+    Self::GenesisLiquidity(event)
+  }
+}
+impl From<economic_security::Event> for Event {
+  fn from(event: economic_security::Event) -> Self {
+    Self::EconomicSecurity(event)
+  }
+}
+impl From<in_instructions::Event> for Event {
+  fn from(event: in_instructions::Event) -> Self {
+    Self::InInstructions(event)
+  }
+}