The producers of “Jury Duty” found Ronald Gladden — the jury foreman unaware that an entire fictional trial was put on for his benefit — via Craigslist. But everyone else in the courtroom was cast through a scripted process, albeit not one that casting director Susie Farris ever used before. The unconventional hybrid nature of “Jury Duty” led Farris and the show’s producers down a very life-meets-art path to find gifted improvisers who could hit the level of absurdity the show demanded without making Gladden suspicious.