Add cpdef declarations in pxd files when overwriting a cdef method #23227
Description
See cython/cython#1732.
Upstream: Fixed upstream, but not in a stable release.
CC: @saraedum
Component: cython
Author: David Roe
Branch/Commit: 919de01
Reviewer: Jeroen Demeyer
Issue created by migration from https://trac.sagemath.org/ticket/23227