How is it possible that every year Adam Gopnik writes a book even better than his last one?  And how is it possible, on the evidence in The Table Comes First (Knopf, $25.95), that he has so much time after his day job at The New Yorker that he makes three different rice puddings, each with its own meaning and savor?  Who before Gopnik has rhapsodized about the English essayist Elizabeth Pannell, a stout Victorian food writer who reveled in gluttony as a “cardinal virtue”?   A hedonist unabashedly addicted to discovering an infinite number of ways to combine saturated fat, sugar, starch, and salt to produce ecstatic pleasure, Gopnik is as pragmatic as he is humorous, a sophisticate with a favorite meal of salmon, broccoli, and brown rice.  Anyone who enjoys eating will completely relish Gopnik’s report from the kitchen, a Manhattan workspace enhanced by the presence of the family dog, Butterscotch.