Nearly 1,500 city workers lost their jobs Friday after failing to comply with a mandate that they are vaccinated for COVID — a bloodletting that included dismissals from the ranks of the NYPD, FDNY and the Department of Education. While staggering in their sheer number, the firings were a long time in the making. Mayor Adams’ predecessor, former Mayor Bill de Blasio, announced the vaccine mandate for city workers in October. Adams kept it in place when he took office, and by Friday, the city had hit a key milestone: for nearly 3,500 city workers, it was either time to show proof of inoculation…