downsampling reflectance returns float64 values

[d-v-b]

We should cast the result of downsampling to the data type of the source data.

[d-v-b]

although we are not ensuring that the result of downsampling has the same type as the input, the actual cause of saving reflectance as float64 is the failure to propagate the encoding (scale + offset) for these data variables.

[emmanuelmathot]

Thank you for the heads up! Can you own this?

[d-v-b]

yes, its fixed in a branch i will submit soon as a pr

[d-v-b]

closed by #75