HONG KONG : Unity Software Inc, the U.S. developer best known for software used to design video games, is in talks to spin off its China unit to help it expand in the world's biggest games market, four people with knowledge of the matter told Reuters. San Francisco-based Unity has sought strategic investors to join it in a business valued at over $1 billion during talks, said two of the people, declining to be identified as they were not authorised to speak publicly on the matter. Unity declined to comment. The talks come as strained Sino-U.S. relations exacerbate sensitivities over…