It all began in Rio On the night of June 30, 1886, Arturo Toscanini — recently turned 19 — arrived, barely on time, at the imperial opera house in Rio de Janeiro, was to perform “Aida.” Pandemonium. The unpopular lead conductor had resigned in a huff; the audience shouted his unpopular replacement off the podium. Toscanini, the principal cellist & assistant choral master, was thrust forward by his colleagues.  “Everyone knew about my memory,” he would recall, “because the singers had all had lessons with me, and I had played the piano without ever looking at the music.”   For the remaining…