What is the fastest way to checkmate/helpmate white(A helpmate is a type of chess problem in which both sides cooperate in order to achieve the goal of checkmating Black/White) in this given position? It is black to play.
Fen: 8/7p/8/8/2k5/6P1/7P/7K b - - 0 1
Bonus Question: Can you find the fastest way to checkmate white without promoting the black lone black pawn?