By RICARDO CASTILLO Maybe Mexican boxer Saúl “Canelo” Álvarez never saw the saga of movies on trigger-happy detective “Dirty Harry,” as wonderfully portrayed by that always-well-admired actor Clint Eastwood. In several of those movies, somewhere near the end, after beating an apparently unbeatable criminal, Dirty Harry would tell the previously invincible crook: “A man’s gotta know his limitations.” Bang! Actually,