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/pallet/Cargo.toml

@@ -29,6 +29,8 @@ frame-support = { git = "https://github.com/serai-dex/substrate", default-featur
 serai-primitives = { path = "../../serai/primitives", default-features = false }
 in-instructions-primitives = { path = "../primitives", default-features = false }
 
+tokens-pallet = { path = "../../tokens/pallet", default-features = false }
+
 [features]
 std = [
   "thiserror",
@@ -47,5 +49,7 @@ std = [
 
   "serai-primitives/std",
   "in-instructions-primitives/std",
+
+  "tokens-pallet/std",
 ]
 default = ["std"]