https://docs.python.org/3/reference/datamodel.html?highlight=__round__#object.__round__

We should define these special methods so that the built-in round and math.trunc, math.floor, math.ceil can operate on Sage numbers.

This can help to eliminate imports of floor and ceil from sage.functions throughout the Sage library, which pulls in all of sage.symbolic.

Related: In the global namespace, we have:

• round = sage.misc.functional.round,
• floor = sage.functions.other.floor,
• ceil = sage.functions.other.ceil,
• trunc - undefined

CC: @jdemeyer @tscrim

Component: python3

Author: Frédéric Chapoton

Branch/Commit: public/ticket/25827 @ 53280c5

Issue created by migration from https://trac.sagemath.org/ticket/25827