Remove −80 dB clipping when plotting backscatter histograms

Backscatter values below -80 dB, when present, are clipped to -80 dB and plotted in the backscatter histogram without informing the user, which may appear as a processing bug. We should remove this clipping.

Example: figure from issue #150:

<img width="1021" height="824" alt="Image" src="https://github.com/user-attachments/assets/6ca09855-9e56-4186-9fdb-b6f01d541e75" />