A development deal with Biogen Inc. could eventually bring City Therapeutics Inc. about $1 billion in milestone payments. It’s a step in the direction the company had been going: looking for the right partners, including those from big pharma. Privately held City Therapeutics is getting $46 million in the deal. That includes $16 million as an up-front payment and an investment of $30 million in exchange for a City Therapeutics convertible note.