change default value for quantization from true to false as it can lead to some crashes (to heavy on ram ?)

get mean and sd by band with random subset if no metadata to avoid loading the entire raster (default hardcoded behaviour for now)

from rasterio 1.4, merge() method does not take `datasets` parameter but `sources` parameter

remove nan during projection fit and replace with mean value during inference. should fix #14 for projections