By day, Boris Berian took orders at the fast-food counter, flipped burgers and cooked fries to make ends meet.By dusk, he trained to become one of the fastest 800-meter runners in the United States.Now, he wonders if all that hard work will really pay off. Berian’s biggest opponent these days isn’t on the track, but in the courtroom. A lawsuit filed by Nike dealing with what sort of gear Berian wears threatens to derail what looked like a for-sure trip to the Rio de Janeiro Olympics this summer.And to think …