(Credit: © The Royal Opera / Clive Barda) Covent Garden has a good line in Verdi revivals – Richard Eyre’s “Traviata” has been running over a quarter of a century; David McVicar’s “Rigoletto” lasted nearly two decades; and now Phyllida Lloyd’s “Macbeth” returns too, also nearly 20 years old. It’s a production that has aged gracefully, with no signs of wear. Though chock {…}