Some business owners struggling to hire workers are lining up behind Gov. Chris Sununu’s plan to use $100 million in federal funds to increase the state’s housing stock. In the two months since Sununu announced the initiative, the state’s unemployment rate has fallen to 2.5% while the vacancy rate for a two-bedroom apartment fell to under 1%. That’s been tough on companies like Boyce Highlands, which makes architectural moldings in Concord and recently acquired a lumber company in Brentwood. While New Hampshire is one of the region’s fastest growing states, the lack of affordable housing continues to be an obstacle, said Taylor Caswell, commissioner of the Department of Business and Economic Affairs.