Tokens pallet (#243)

* Use Monero-compatible additional TX keys

This still sends a fingerprinting flare up if you send to a subaddress which
needs to be fixed. Despite that, Monero no should no longer fail to scan TXs
from monero-serai regarding additional keys.

Previously it failed becuase we supplied one key as THE key, and n-1 as
additional. Monero expects n for additional.

This does correctly select when to use THE key versus when to use the additional
key when sending. That removes the ability for recipients to fingerprint
monero-serai by receiving to a standard address yet needing to use an additional
key.

* Add tokens_primitives

Moves OutInstruction from in-instructions.

Turns Destination into OutInstruction.

* Correct in-instructions DispatchClass

* Add initial tokens pallet

* Don't allow pallet addresses to equal identity

* Add support for InInstruction::transfer

Requires a cargo update due to modifications made to serai-dex/substrate.

Successfully mints a token to a SeraiAddress.

* Bind InInstructions to an amount

* Add a call filter to the runtime

Prevents worrying about calls to the assets pallet/generally tightens things
up.

* Restore Destination

It was meged into OutInstruction, yet it didn't make sense for OutInstruction
to contain a SeraiAddress.

Also deletes the excessively dated Scenarios doc.

* Split PublicKey/SeraiAddress

Lets us define a custom Display/ToString for SeraiAddress.

Also resolves an oddity where PublicKey would be encoded as String, not
[u8; 32].

* Test burning tokens/retrieving OutInstructions

Modularizes processor_coinUpdates into a shared testing utility.

* Misc lint

* Don't use PolkadotExtrinsicParams

substrate/tokens/primitives/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "tokens-primitives"
+version = "0.1.0"
+description = "Serai tokens primitives"
+license = "MIT"
+authors = ["Luke Parker <lukeparker5132@gmail.com>"]
+edition = "2021"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
+[dependencies]
+scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }
+scale-info = { version = "2", default-features = false, features = ["derive"] }
+
+serde = { version = "1", features = ["derive"], optional = true }
+
+serai-primitives = { path = "../../serai/primitives", default-features = false }
+
+[dev-dependencies]
+sp-runtime = { git = "https://github.com/serai-dex/substrate", default-features = false }
+
+[features]
+std = ["scale/std", "scale-info/std", "serde", "sp-runtime/std", "serai-primitives/std"]
+default = ["std"]

substrate/tokens/primitives/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2023 Luke Parker
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

substrate/tokens/primitives/src/lib.rs

@@ -0,0 +1,33 @@
+#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use scale::{Encode, Decode, MaxEncodedLen};
+use scale_info::TypeInfo;
+
+#[cfg(feature = "std")]
+use serde::{Serialize, Deserialize};
+
+use serai_primitives::{SeraiAddress, ExternalAddress, Data, pallet_address};
+
+pub const ADDRESS: SeraiAddress = pallet_address(b"Tokens");
+
+#[derive(Clone, PartialEq, Eq, Debug, Encode, Decode, MaxEncodedLen, TypeInfo)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub struct OutInstruction {
+  pub address: ExternalAddress,
+  pub data: Option<Data>,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, Encode, Decode, MaxEncodedLen, TypeInfo)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub enum Destination {
+  Native(SeraiAddress),
+  External(OutInstruction),
+}
+
+#[test]
+fn address() {
+  use sp_runtime::traits::TrailingZeroInput;
+  assert_eq!(ADDRESS, SeraiAddress::decode(&mut TrailingZeroInput::new(b"Tokens")).unwrap());
+}