“The mattress is a canvas. For most of Future's career, vacuum-sealed packages and hastily-stuffed fistfuls of money have played on a continuous loop, while sex, love, and heartbreak take the foreground. (He hasn’t merged the bed’s many uses the way Havoc did with “Blow you off the atlas as if I caught you fucking my wife on my thousand dollar mattress,” but really, who has?) On “Inside the Mattres”