Mezzo-soprano Anita Rachvelishvili, who sings the role of Santuzza in the Chicago Symphony Orchestra’s concert presentations of Mascagni’s “Cavalleria rusticana” on Feb. 6-8, calls the work “a typical operatic story, where somebody dies at the end … but the music holds it together. And the music of ‘Cavalleria rusticana’ is something very special.”