In this ticket we equip scalar fields with a method copy_from as we did for tensor fields in #28628.

CC: @egourgoulhon @tscrim

Component: manifolds

Keywords: scalarfields

Author: Michael Jung

Branch/Commit: e15fbf3

Reviewer: Travis Scrimshaw, Samuel Lelièvre

Issue created by migration from https://trac.sagemath.org/ticket/31654