CAIRO — At least 54 police officers, including 20 officers and 34 conscripts, were killed when a raid on a militant hideout southwest of Cairo escalated into an all-out firefight, authorities said Saturday, in one of the single deadliest attacks by militants against Egyptian security forces in recent years. The officials said the exchange of fire began late Friday in the al-Wahat al-Bahriya area in Giza province, about 84 miles southwest of Cairo. The firefight began when security forces acting on intelligence moved against a militants’ hideout in the area.