ROME — On a sunny Tuesday afternoon in the Trastevere neighborhood, Sophie Minchilli marveled at the number of people teeming in every piazza and restaurant. The guide and food tour company co-founder said that after the Easter holiday rush, April tends to be a quiet time in the city. Not this year. Peak tourist season in Rome is expanding, creeping into the early days of spring and stretching through the fall — good news for tour guides and bad news for price-sensitive travelers.