feat: port GroupTheory.Torsion (#4321)

Author: mattrobball

Mathlib.lean

@@ -1557,6 +1557,7 @@ import Mathlib.GroupTheory.Subsemigroup.Center
 import Mathlib.GroupTheory.Subsemigroup.Centralizer
 import Mathlib.GroupTheory.Subsemigroup.Membership
 import Mathlib.GroupTheory.Subsemigroup.Operations
+import Mathlib.GroupTheory.Torsion
 import Mathlib.InformationTheory.Hamming
 import Mathlib.Init.Algebra.Classes
 import Mathlib.Init.Algebra.Functions