Rush’s Alex Lifeson spent decades as one of rock’s most brilliantly productive stoners. He always played concerts sober, but half-joked to me in 2015 that he wrote “80 percent” of his oft-labyrinthine parts for Rush’s music with THC assistance. But this year, with a high-pressure reunion tour looming, he finally quit weed, as he revealed in our recent cover story interview, published in collaboration with Rolling Stone Canada. “I started having …