Thursday was 93-degree New York at its most relentless. Hung-over Knicks fans collided on the morning subway with tourists in soccer jerseys coming in for the World Cup.   For the 50 or so people in a cool Brooklyn courtroom, the delirium outside was nonexistent. They remained anchored to the horrors of 2020, and the city’s 47% spike that year in murders.   The proceeding was straightforward: Judge Deepa Ambekar sentenced 30-year-old William Freeman to 18 years in prison on a manslaughter plea,