BOSTON - Real-life BFFs Daveed Diggs and Rafael Casal – stars and co-writers of the comedy-drama “Blindspotting” – spent the night before our interview hosting a question-and-answer session after their movie screened at Somerville Theater as part of the International Film Festival of Boston. They stuck around, taking selfies with fans, even phoning co-star Jasmine Cephas Jones via FaceTime to answer a question from the audience.