Walking into the Lamplighter Brewing Company in Cambridge on an early Saturday afternoon, it would be easy to forget that it’s a brewery and taproom.The space is lined with local college students with their laptops open, working on homework and drinking espressos and cold-brewed coffee.That’s because the Lamplighter, 284 Broadway, is home to Longfellows Coffee during the mornings and early afternoons, bringing a crossover crowd of beer and coffee lovers.