l2gen: improve handling of saturation

The OCI L1B data sets a band dependent flag when the band saturates. This saturation doesn't necessarily require setting the HILT flag, as processing may continue without issue depending on the products to be generated. We need to figure out how to make l2gen band-dependent-saturation aware. The reader should set the band to fill when saturated, but the algorithms need that may use these bands need to properly handle this condition