Lines snake around the block on most mornings outside of New England Treatment Access, a marijuana store in Brookline’s quaint retail district, even though the owners have tried to alleviate the problem by encouraging online advance ordering. The store has been open for five months. Massachusetts has 23 legal pot stores and lines are common on weekends at many. The Brookline NETA store often sees 2,500 customers a day, making it among the top producing stores in the country.