Amid a flurry of dealmaking activity to start 2024, Allorion Therapeutics Inc., a 2020 startup based in Natick, Mass., and Guangzhou, China, has been extra busy. Two days after disclosing a potential $540 million deal with Astrazeneca plc, Allorion inked a licensing agreement with Avenzo Therapeutics Inc. that could total more than $1 billion.