Add Substrate "assets" pallet

While over-engineered for our purposes, it's still usable.

Also cleans the runtime a bit.

substrate/serai/primitives/src/amount.rs

@@ -0,0 +1,31 @@
+use core::{ops::{Add, Mul}};
+
+use scale::{Encode, Decode, MaxEncodedLen};
+use scale_info::TypeInfo;
+#[cfg(feature = "std")]
+use serde::{Serialize, Deserialize};
+
+/// The type used for amounts.
+#[derive(
+  Clone, Copy, PartialEq, Eq, PartialOrd, Debug, Encode, Decode, TypeInfo, MaxEncodedLen,
+)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub struct Amount(pub u64);
+
+/// One whole coin with eight decimals.
+#[allow(clippy::inconsistent_digit_grouping)]
+pub const COIN: Amount = Amount(1_000_000_00);
+
+impl Add for Amount {
+  type Output = Amount;
+  fn add(self, other: Amount) -> Amount {
+    Amount(self.0 + other.0)
+  }
+}
+
+impl Mul for Amount {
+  type Output = Amount;
+  fn mul(self, other: Amount) -> Amount {
+    Amount(self.0 * other.0)
+  }
+}

substrate/serai/primitives/src/coins.rs

@@ -0,0 +1,19 @@
+use scale::{Encode, Decode, MaxEncodedLen};
+use scale_info::TypeInfo;
+#[cfg(feature = "std")]
+use serde::{Serialize, Deserialize};
+
+/// The type used to identify coins.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub struct Coin(pub u32);
+impl From<u32> for Coin {
+  fn from(coin: u32) -> Coin {
+    Coin(coin)
+  }
+}
+
+pub const BITCOIN: Coin = Coin(0);
+pub const ETHER: Coin = Coin(1);
+pub const DAI: Coin = Coin(2);
+pub const MONERO: Coin = Coin(3);

substrate/serai/primitives/src/lib.rs

@@ -1,36 +1,7 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
-use core::ops::{Add, Mul};
+mod amount;
+pub use amount::*;
 
-use scale::{Encode, Decode, MaxEncodedLen};
-use scale_info::TypeInfo;
-#[cfg(feature = "std")]
-use serde::{Serialize, Deserialize};
-
-/// The type used for amounts.
-#[derive(Clone, Copy, PartialEq, Eq, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
-#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
-pub struct Amount(pub u64);
-
-impl Add<Amount> for Amount {
-  type Output = Amount;
-  fn add(self, other: Amount) -> Amount {
-    Amount(self.0 + other.0)
-  }
-}
-
-impl Mul<Amount> for Amount {
-  type Output = Amount;
-  fn mul(self, other: Amount) -> Amount {
-    Amount(self.0 * other.0)
-  }
-}
-
-/// One whole coin with eight decimals.
-#[allow(clippy::inconsistent_digit_grouping)]
-pub const COIN: Amount = Amount(1_000_000_00);
-
-/// The type used to identify coins.
-#[derive(Clone, Copy, PartialEq, Eq, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
-#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
-pub struct Coin(pub u32);
+mod coins;
+pub use coins::*;