When the Hanwha Classic, a 10-year-old concert series that highlights Baroque music, returns this year with a top Italian ensemble and star mandolinist, it will be offering a rare chance not only for period music fans but also for the musicians who continue to evolve to enjoy Baroque music. Titled “Unity: Il Giardino Armonico and Avi Avital,” the concerts will take place Tuesday and Wednesday at the Conce.