Some of the city’s biggest big box stores are moving or closing shop, creating once-in-a-decade opportunities in an already hot retail leasing market. “The market is rocking — this is when it’s fun,” said Brandon Singer of Retail by Mona. “The market is super strong and there’s a ton of deal velocity.” Earlier this month, outdoor lifestyle brand REI announced that it will vacate its longtime home at Kushner Companies’ Puck Building at Lafayette Street and Houston when its lease runs out at the