Add Dex pallet (#407)

* Move pallet-asset-conversion

* update licensing

* initial integration

* Integrate Currency & Assets types

* integrate liquidity tokens

* fmt

* integrate dex pallet tests

* fmt

* compilation error fixes

* integrate dex benchmarks

* fmt

* cargo clippy

* replace all occurrences of "asset" with "coin"

* add the actual add liq/swap logic to in-instructions

* add client side & tests

* fix deny

* Lint and changes

- Renames InInstruction::AddLiquidity to InInstruction::SwapAndAddLiquidity
- Makes create_pool an internal function
- Makes dex-pallet exclusively create pools against a native coin
- Removes various fees
- Adds new crates to GH workflow

* Fix rebase artifacts

* Correct other rebase artifact

* Correct CI specification for liquidity-tokens

* Correct primitives' test to the standardized pallet account scheme

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

substrate/liquidity-tokens/pallet/src/lib.rs

@@ -0,0 +1,152 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[frame_support::pallet]
+pub mod pallet {
+  use sp_core::sr25519::Public;
+  use sp_std::vec::Vec;
+  use frame_support::pallet_prelude::*;
+
+  use dex_primitives::LiquidityTokens;
+  use serai_primitives::*;
+
+  #[pallet::config]
+  pub trait Config: frame_system::Config<AccountId = Public> {
+    type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;
+  }
+
+  #[pallet::error]
+  pub enum Error<T> {
+    AmountOverflowed,
+    NotEnoughCoins,
+  }
+
+  #[pallet::event]
+  #[pallet::generate_deposit(fn deposit_event)]
+  pub enum Event<T: Config> {
+    LtMint { to: Public, token: u32, amount: Amount },
+    LtBurn { from: Public, token: u32, amount: Amount },
+  }
+
+  #[pallet::pallet]
+  pub struct Pallet<T>(PhantomData<T>);
+
+  /// The amount of coins each account has.
+  // Identity is used as the second key's hasher due to it being a non-manipulatable fixed-space
+  // ID.
+  #[pallet::storage]
+  #[pallet::getter(fn balances)]
+  pub type Balances<T: Config> = StorageDoubleMap<
+    _,
+    Blake2_128Concat,
+    Public,
+    Blake2_128Concat,
+    u32,
+    SubstrateAmount,
+    OptionQuery,
+  >;
+
+  /// The total supply of each coin.
+  // We use Identity type here again due to reasons stated in the Balances Storage.
+  #[pallet::storage]
+  #[pallet::getter(fn supply)]
+  pub type Supply<T: Config> = StorageMap<_, Blake2_128Concat, u32, SubstrateAmount, ValueQuery>;
+
+  // TODO: apis: supply, mint, burn, transfer
+  impl<T: Config> Pallet<T> {
+    /// Returns the balance of a given account for `token`.
+    pub fn balance(token: u32, of: T::AccountId) -> SubstrateAmount {
+      Self::balances(of, token).unwrap_or(0)
+    }
+
+    /// Mint `balance` to the given account.
+    ///
+    /// Errors if any amount overflows.
+    pub fn mint_into(token: u32, to: Public, amount: SubstrateAmount) -> Result<(), Error<T>> {
+      let balance = Self::balances(to, token).unwrap_or(0);
+
+      // update the balance
+      let new_amount = balance.checked_add(amount).ok_or(Error::<T>::AmountOverflowed)?;
+
+      // save
+      Balances::<T>::set(to, token, Some(new_amount));
+
+      // update the supply
+      let new_supply =
+        Self::supply(token).checked_add(amount).ok_or(Error::<T>::AmountOverflowed)?;
+      Supply::<T>::set(token, new_supply);
+
+      Self::deposit_event(Event::LtMint { to, token, amount: Amount(amount) });
+      Ok(())
+    }
+
+    // Burn `balance` from the specified account.
+    pub fn burn_from(token: u32, from: Public, amount: SubstrateAmount) -> Result<(), Error<T>> {
+      let balance = Self::balances(from, token);
+      if balance.is_none() {
+        Err(Error::<T>::NotEnoughCoins)?;
+      }
+
+      // update the balance
+      let new_amount = balance.unwrap().checked_sub(amount).ok_or(Error::<T>::NotEnoughCoins)?;
+
+      // save
+      if new_amount == 0 {
+        Balances::<T>::remove(from, token);
+      } else {
+        Balances::<T>::set(from, token, Some(new_amount));
+      }
+
+      // update the supply
+      let new_supply = Self::supply(token).checked_sub(amount).unwrap();
+      if new_supply == 0 {
+        Supply::<T>::remove(token);
+      } else {
+        Supply::<T>::set(token, new_supply);
+      }
+
+      Self::deposit_event(Event::LtBurn { from, token, amount: Amount(amount) });
+      Ok(())
+    }
+
+    pub fn total_issuance(token: u32) -> SubstrateAmount {
+      Supply::<T>::get(token)
+    }
+  }
+
+  impl<T: Config> LiquidityTokens<T::AccountId> for Pallet<T> {
+    type Balance = SubstrateAmount;
+    type CoinId = u32;
+
+    fn mint_into(
+      token: Self::CoinId,
+      to: &Public,
+      amount: Self::Balance,
+    ) -> Result<Self::Balance, DispatchError> {
+      Self::mint_into(token, *to, amount)?;
+      Ok(amount)
+    }
+
+    fn burn_from(
+      token: Self::CoinId,
+      from: &Public,
+      amount: Self::Balance,
+    ) -> Result<Self::Balance, DispatchError> {
+      Self::burn_from(token, *from, amount)?;
+      Ok(amount)
+    }
+
+    fn total_issuance(token: Self::CoinId) -> Self::Balance {
+      Self::total_issuance(token)
+    }
+
+    fn coin_ids() -> Vec<Self::CoinId> {
+      Supply::<T>::iter_keys().collect::<Vec<Self::CoinId>>()
+    }
+
+    fn balance(token: Self::CoinId, of: &Public) -> Self::Balance {
+      Self::balance(token, *of)
+    }
+  }
+}
+
+pub use pallet::*;