Sema4 Holdings Corp. sent a bold message to the market with a definitive agreement to acquire Genedx Inc. from Opko Health Inc. for $623 million. The deal comes as Sema4 winds down its COVID-19 testing by the end of March. The company has been one of the largest testing organizations in Connecticut since its first contract in May 2020, but has lately come under scrutiny because of an investment by Annie Lamont, the governor’s wife.