After having a week off between the regular-season finale and Game 1 of the playoffs, the Boston Celtics are itching to get back onto the court. They’ve been preparing for the Brooklyn Nets since Tuesday night, and come Sunday afternoon, they’ll be ready to burst out of the tunnel at TD Garden. “You can tell the group is ready to play,” head coach Ime Udoka said following practice Saturday afternoon. “The rest is needed and is good, but at some point, you start to get a little jittery and ready to play after this much time off and knowing what’s coming up. So you can feel the anticipation and our guys are ready to roll.”