Improve 1d binning plots

[adehecq]

Currently, the function xdem.spatialstats.plot_1d_binning only shows one metric at a time, with a scatter plot.

It would be useful to at least show a central tendency + dispersion (e.g. median + NMAD) as a barplot. Ideally, we could even make a violin plot like Fig 4 in Hugonnet et al. (2022), but this would probably need to be a separate function as it requires the full array of values.

[adehecq]

We could also consider a higher-level function that plot a set of 1d plots for a given DEM difference, e.g. showing barplots/violin plots of dh vs slope, curvature, elevation, along-track etc. Just to make it easy to identify bias patterns in the data.

[rhugonnet]

I like the summary plot idea 😄
All of these should be relatively small effort