Given a list of tuples of client and appointment length and several constraints, print out a client's schedule consisting of both appointments and breaks.
Implement build_schedule(appointments, day_start, day_end, break_length). Each appointment is [client, duration], and times are integer units such as minutes from midnight. Return a list of [label, start, end] entries, inserting one "Break" entry between consecutive appointments. Inputs are valid, and the completed schedule must not extend past day_end.
def build_schedule(appointments, day_start, day_end, break_length):