Powers of -1 in the center of a preadditive category

@[simp]

theorem CategoryTheory.CatCenter.app_neg_one_zpow {C : Type u} [Category.{v, u} C] [Preadditive C] (n : ℤ) (X : C) : (↑((-1) ^ n)).app X = n.negOnePow • CategoryStruct.id X