Sentinel-1 scaling to UINT16 for Orfeo contains a bug

[kvantricht]

As a long-standing issue, Orfeo has the problem that values below thermal noise are treated the same way as nodata and both end up being "0" (Open-EO/openeo-geopyspark-driver#293). OpenEO treats both as nodata.

The current compress_backscatter_uint16 logic tried to cope with this by including an if_ and setting nodata values to 1 (https://github.com/Open-EO/openeo-gfmap/blob/main/src/openeo_gfmap/preprocessing/sar.py#L34-L51). This is however unsafe because this way, not only off-swath nodata values get replaced, but if the compression is applied e.g. after aggregate_temporal_period, any missing timestamps also get filled with in this case the value 1.

So below thermal noise and real nodata will always have to be treated in an identical way until this is handled in a better way on Orfeo side. I suggest after considerable testing that we remove the Orfeo-specific logic and the if_ statement and keep all nodata as nodata.