Add internal padding instruction

gbso/insn.py

@@ -1070,3 +1070,12 @@ class SCF(Insn):
 
     def pretty(self) -> str:
         return "SCF"
+
+
+@dataclass
+class UNUSED(Insn):
+    def exec(self, cpu: CPU) -> None:
+        pass
+
+    def pretty(self) -> str:
+        return "UNUSED"