Update develop to patch-polkadot-sdk

Allows us to finally remove the old `serai-dex/substrate` repository _and_
should have CI pass without issue on `develop` again.

The changes made here should be trivial and maintain all prior
behavior/functionality. The most notable are to `chain_spec.rs`, in order to
still use a SCALE-encoded `GenesisConfig` (avoiding `serde_json`).

processor/messages/src/lib.rs

@@ -1,3 +1,5 @@
+#![expect(clippy::cast_possible_truncation)]
+
 use std::collections::HashMap;
 
 use scale::{Encode, Decode};