Use a transcript when generating the per-chain binding for a given set of keys

While it was fine as-is, as it only had one variable length property, 
this is a bit more robust. Also binds the Curve ID, which should declare 
differently even for just different basepoints, and therefore adds two 
variable length properties (justifying the transcript).

processor/Cargo.toml

@@ -14,6 +14,7 @@ thiserror = "1"
 curve25519-dalek = { version = "3", features = ["std"] }
 blake2 = "0.10"
 
+transcript = { path = "../crypto/transcript" }
 dalek-ff-group = { path = "../crypto/dalek-ff-group" }
 frost = { path = "../crypto/frost" }