feat: port RingTheory.Valuation.Basic (#2846)

Co-authored-by: Matthew Ballard <matt@mrb.email>

Author: RemyDegenne

Mathlib.lean

@@ -1274,6 +1274,7 @@ import Mathlib.RingTheory.Subring.Basic
 import Mathlib.RingTheory.Subring.Pointwise
 import Mathlib.RingTheory.Subsemiring.Basic
 import Mathlib.RingTheory.Subsemiring.Pointwise
+import Mathlib.RingTheory.Valuation.Basic
 import Mathlib.SetTheory.Cardinal.Basic
 import Mathlib.SetTheory.Cardinal.Cofinality
 import Mathlib.SetTheory.Cardinal.Continuum