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/in-instructions/primitives/Cargo.toml

@@ -16,10 +16,9 @@ scale-info = { version = "2", default-features = false, features = ["derive"] }
 
 serde = { version = "1", features = ["derive"], optional = true }
 
-sp-core = { git = "https://github.com/serai-dex/substrate", default-features = false }
-
 serai-primitives = { path = "../../serai/primitives", default-features = false }
+tokens-primitives = { path = "../../tokens/primitives", default-features = false }
 
 [features]
-std = ["scale/std", "scale-info/std", "serde", "sp-core/std", "serai-primitives/std"]
+std = ["scale/std", "scale-info/std", "serde", "serai-primitives/std", "tokens-primitives/std"]
 default = ["std"]