HONG KONG — The robotics firm behind China’s famously backflipping humanoids leapt to a remarkable stock market debut on Wednesday, with Unitree’s shares closing up 460% as investors rally behind homegrown beneficiaries of the A.I. boom.Chinese humanoid and other robots have advanced at a breathtaking pace as Beijing competes for global tech dominance with Washington, which banned imports of new foreign-made robots last month over national security concerns. Unitree, the first humanoid robotics maker to go public on a mainland Chinese exchange, has won global attention with its humanoid and quadruped robots that can run, dance, and do backflips and…