By Valentyn Ogirenko and Aziz El Yaakoubi KYIV/RIYADH (Reuters) – President Volodymyr Zelenskiy hailed as “superheroes” the senior Ukrainian commanders, including those who led the dogged defence of Mariupol, who were freed by Russia as part of an unexpected prisoner swap involving almost 300 people, including foreigners. Under the terms of the deal, which Turkey helped to broker, 215 Ukrainians – most of whom were captured after the fall of the port city – were released on Wednesday. In exchange, Ukraine sent back 55 Russians and pro-Moscow Ukrainians. Ten foreigners were also freed following…