(Photo: Marc Brenner) They go together like cookies and milk…like bacon and eggs…like Adam and Eve! Nooooooo! Not “Cav” and “Pag,” as the fans insist on calling the operas, but Roberto Alagna and Aleksandra Kurzak! The golden couple, currently on at the Royal Opera House in “Cavalleria Rusticana,” consolidated their positions as world class artists here with spellbinding performances from {…}