add cancelTransaction method to salepoint CC API

Author: techno-sam

common/src/main/java/dev/ithundxr/createnumismatics/compat/computercraft/implementation/peripherals/SalepointPeripheral.java

@@ -132,6 +132,11 @@ public final void startTransaction(String accountID, String authorizationID, int
             throw new LuaException("Failed to start transaction");
     }
 
+    @LuaFunction(mainThread = true)
+    public final void cancelTransaction() {
+        blockEntity.cancelTransaction();
+    }
+
     @Override
     public String getType() {
         return "Numismatics_Salepoint";