Documentaries about partially quirky niche subjects have to tread carefully unless the narrative has a “stranger than fiction” angle.  Science Fair filmmakers Cristina Costantini and Darren Foster set the stage for their tone awfully fast by opening up their doc with the purity and lucrative opportunities that comes with winning “Best in Fair” at the prestigious Intel ISEF (International Science and Engineering Fair);  giving audiences a taste of the inspiration and the exposure this film…