Fix cpdef declaration issues in modular and number fields

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Part of #23600.

CC:  @roed314

Component: **cython**

Author: **David Roe, Jeroen Demeyer**

Branch/Commit: **[`4f6ba69`](https://github.com/sagemath/sagetrac-mirror/commit/4f6ba690f6387f5e272f476974555cf07c6ac137)**

Reviewer: **David Roe**

_Issue created by migration from https://trac.sagemath.org/ticket/23603_

