A knife-wielding maniac with a history of mental illness and 53 prior arrests is wanted in connection with at least two stabbings in the subway this week, The Post has learned. Cops searching for Jamar Banks were warned to use “extreme caution” when encountering him because he is believed to be armed with “a large knife,” according to a message sent to police officers and obtained by The Post. Banks, 52, is known to frequent the No. 2 and No. 5 subway lines, authorities said in the message. He’s being sought in connection with stabbings on Jan. 1 and Jan....