More than a year after the Boston Marathon bombings, a Boylston Street print shop has turned to the courts in an attempt to force its insurance company to cover the financial losses it says it sustained as a result of the attack. The lawsuit, filed last month in Suffolk Superior Court, turns on the question of whether the terrorism insurance Sir Speedy printing carried — and paid extra for — should cover business losses and other costs incurred while the print shop was shut for 14 days after the bombing.