A vicious fire inside a violation-plagued Queens building that killed four people — including a toddler — is now being investigated as a homicide, cops said Sunday. The deaths of four people in the March 16 blaze that tore through 132-05 Avery Ave. in Flushing were deemed a homicide by the Office of the Chief Medical Examiner. Both the police and fire department’s investigations into the blaze remain ongoing, and there are no arrests at this time, officials said.  The inferno incinerated the