A construction company is suing the developers behind an ambitious housing project, once expected to transform a troubled Portland neighborhood, for fraud. In a federal lawsuit, a Vermont construction firm claims that the developers of the proposed Midtown complex have broken contracts and been playing a corporate “shell game” to avoid paying for more than $235,000 worth of work on the $85 million project that’s been held up for year. Since 2013, PC Construction Company has held a series of contracts to do preliminary work for the Midtown developers, who initially proposed putting hundreds of apartments, commercial space and a parking garage on 3.25 acres of vacant industrial land in the Bayside neighborhood.