NEW YORK — New York City rat sighting rates have reached the stRATosphere. In the first nine months of this year, the city fielded almost 21,600 rat complaints, a tally about 71% higher than the count reported at the same point in 2020, according to rattling government data. City officials are scrambling to root out increasingly bold rats — boundless in their ranks — who pop out from under stoops and scurry along sidewalks. But early government efforts to derail the rodents, including a program to demolish dilapidated outdoor dining sheds, have yet to produce obvious improvements. The city exp…