By Casey Hall SHANGHAI (Reuters) -China on Saturday marked the first day of “chun yun”, the 40-day period of Lunar New Year travel known pre-pandemic as the world’s largest annual migration of people, bracing for a huge increase in travellers and the spread of COVID-19 infections. This Lunar New Year public holiday, which officially runs from Jan. 21, will be the first since 2020 without domestic travel restrictions. Over the last month China has seen the dramatic dismantling of its “zero-COVID” regime following historic protests against a policy that included frequent testing, restricted move…