With characters like Sherlock Holmes, Julian Assange and Stephen Hawking, Benedict Cumberbatch has accumulated a filmography littered with high IQs. Characters of analytical prowess and fast-deducting intellect have made Cumberbatch something like the ultimate quicksilver mind of the digital age. No actor has made computation sexier. Cumberbatch, relaxing in a Toronto hotel room, quickly points out that he has — like his spineless plantation owner of “12 Years a Slave” or his painfully shy son in “August: Osage County” — played some “pretty dull, ordinary” people: “Let’s say us. I’ve done us, version of me and you,”