Prosecutors on Tuesday asked a federal judge in Boston to reject former House speaker Salvatore F. DiMasi’s request to stay in a Rhode Island detention center while he appeals his conviction on corruption charges, claiming the former lawmaker will burden the US Marshals Service if his request is granted. The former Beacon Hill power broker, who began serving an 8-year prison sentence in November at the Federal Medical Center in Lexington, Ky., was transferred to Wyatt last month.