I'm afraid resource leveling will never do that. The Team Planner view (Project Pro only) allows you to easily see what tasks a resource is assigned to and adjust assignment units if needed. You could set up task calendars so the year long task that is 10 hours is only worked on from 08:00 to 10:00. You could then assign Giovanni at 100% to that task. I guess the other question is - do you need the year long task in your project? Could you set Giovanni's maximum units to 75% and go from there?

Then assign Giovanni at 75% to other tasks and let the leveling command delay tasks of lesser importance.