Use the right category for DefaultConvertMaps, rather than SetsWithPartialMaps #23184
Description
Currently, the category for DefaultConvertMaps is SetsWithPartialMaps().
sage: type(QQ[['x']].coerce_map_from(QQ))
<type 'sage.structure.coerce_maps.DefaultConvertMap_unique'>
sage: QQ[['x']].coerce_map_from(QQ).category_for()
Category of sets with partial maps
In contrast,
sage: QQ.hom(QQ[['x']]).category_for()
Category of euclidean domains
Depends on #23201
Component: coercion
Keywords: sd86.5
Author: David Roe, Julian Rüth
Branch: 5eccb52
Reviewer: Julian Rüth, David Roe
Issue created by migration from https://trac.sagemath.org/ticket/23184