Coat a 9x9-inch glass or metal baking dish with cooking spray. Set aside. Begin to melt the butter and marshmallows together in a large stockpot over medium-low heat, uncovered, about 3 minutes. Stir occasionally with a heat-proof spatula. Add the cocoa powder and the Torani Chocolate Sugar Free Syrup. Stir vigorously with the heat-proof spatula until fully melted and combines, about 2 more minutes. Turn off heat. Add 8 cups of plain puffed rice cereal. Fold to combine. Transfer mixture to the prepared 9x9-inch pan and press with the spatula to evenly distribute. Refrigerate 1 hour or overnight. Place semi sweet chocolate chips in a glass measuring cup and microwave about 1 minute, stirring every 20 seconds. Do not-over cook as the chocolate will separate. Dip a spoon into the melted chocolate and drizzle over the cereal bars. Let sit 10 minutes, and then repeat process with the white chocolate chips. Refrigerate another hour or overnight.