keystore.sign_message: add optional script_type argument

this is used by trezor
(and also by bitbox02, which was using a workaround previously)

fixes https://github.com/spesmilo/electrum/issues/7670

electrum/keystore.py

@@ -127,7 +127,14 @@ class KeyStore(Logger, ABC):
         pass
 
     @abstractmethod
-    def sign_message(self, sequence: 'AddressIndexGeneric', message, password) -> bytes:
+    def sign_message(
+            self,
+            sequence: 'AddressIndexGeneric',
+            message: str,
+            password,
+            *,
+            script_type: Optional[str] = None,
+    ) -> bytes:
         pass
 
     @abstractmethod
@@ -175,7 +182,7 @@ class Software_KeyStore(KeyStore):
     def may_have_password(self):
         return not self.is_watching_only()
 
-    def sign_message(self, sequence, message, password) -> bytes:
+    def sign_message(self, sequence, message, password, *, script_type=None) -> bytes:
         privkey, compressed = self.get_private_key(sequence, password)
         key = ecc.ECPrivkey(privkey)
         return key.sign_message(message, compressed)