Down on the Naubuc flats, where the land lies low and green toward the Connecticut River, July evenings hold the smell of cut grass long after the machines have gone quiet. NERI Services LLC keeps lawns in Glastonbury — mowing, trimming, edging, the ordinary upkeep that makes a yard look tended rather than merely alive. It is repeatable, unglamorous work, and it is exactly what makes a summer street feel cared for. On a hot Thursday the engines shut down one at a time, and the yard is left even, trimmed and still.