Part of #32191 (Meta-ticket: Audit/fix all uses of MixedIntegerLinearProgram in sage.combinat, sage.graphs).

Here we avoid the use of Integer(round(p.solve(...))) whenever possible.

CC: @slel

Component: graph theory

Author: David Coudert

Branch/Commit: cd6bd11

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/32537