What’s most improbable about this 2014 Marvel movie? That it stars Chris Pratt from Parks and Recreation as an action hero? Bradley Cooper as a gun-toting, fast-talking raccoon? Vin Diesel as a monosyllabic giant tree-trunk alien? Zoe Saldana as a green-skinned space warrior? Or that it was a monster hit for Marvel, launching a new franchise from one of the comic company’s least-known titles?