To read the news, one might think that the “perp walk” was a necessary rite in the career of a New York State legislator. Eighteen Albany lawmakers have left office as a result of criminal charges or ethical misconduct since 1999, according to the government-reform organization Citizens Union — a run that the organization appropriately terms a “crime wave.” There are many reasons to account for this dismal record, but one in particular concerns a practice that, at first glance, may seem endearingly quaint: the legislators are part-timers.