MUKALLA, Yemen — They call it the “grill”: The victim is tied to a spit like a roast and spun furiously within a circle of fire. It is just one of the terrors inflicted by interrogators on detainees in Yemen who are routinely beaten with wires and were kept in filthy shipping containers, blindfolded for months – all by one of America’s closest counterterrorism allies. Abuse and torture are rife in a network of secret prisons across southern Yemen where hundreds are detained in the hunt for al-Qaida militants, former detainees say.