Local startup Allostatix has signed a $3.5 million contract with a Texas health benefits management company to help determine the most cost-effective way to test patients with symptoms of obstructive sleep apnea. The deal is the largest ever for Allostatix, which was founded in 2007 and is based at HCDC Inc., the Hamilton County business incubator in Norwood. The five-year contract will generate $700,000 annually for Allostatix, a data analytics firm that develops health care solutions from big…