To close its 2015-16 season, The Atlanta Opera tipped its hat to French Grand opera and unveiled a star-studded production of Gounod’s Romeo et Juliette this past Saturday. While all opera is dependent on singers of not only extraordinary technical pedigree but also of a musical understanding of how language informs declamation, Grand French opera relies on the latter more heavily so, making Romeo et Juliette notoriously difficult to cast. …