“I was a hard case, and it seems like I needed to learn my lesson the hard way,” writes Cameron Douglas, son of actor Michael Douglas, in his affecting memoir of crime and punishment.   The author grew up between well-to-do households where it was a party trick for him as a child to pass a joint among the beautiful people.  By the age of 25, he was injecting cocaine three times an hour while realizing that “the worst-case scenario has already happened,” his opportunities in the show-business world long since tossed away. The worst case, though, had yet to develop: in and out of rehab, as well as the penal system, proceeding from juvenile detention to time in a federal prison full of warring racial factions, all brought on by a fierce addiction to heroin and a drug-selling operation meant to support it.