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).

coins/monero/src/tests/clsag.rs

@@ -96,7 +96,7 @@ fn clsag_multisig() -> Result<(), MultisigError> {
     algorithm_machines(
       &mut OsRng,
       ClsagMultisig::new(
-        Transcript::new(b"Monero Serai CLSAG Test".to_vec()),
+        Transcript::new(b"Monero Serai CLSAG Test"),
         Rc::new(RefCell::new(Some(
           ClsagDetails::new(
             ClsagInput::new(