feat(ring_theory/power_series/basic): Add `rescale_X` (#15397)
feat(ring_theory/power_series/basic): Add `rescale_X` (#15397)




Co-authored-by: Tyler Raven Billingsley <d1787ef6333caf08dc6f0598f50c2affcbe74052@users.noreply.github.com>

leanprover-community/mathlib,leanprover-community/mathlib