[ESSDIFFRACTION] Add ‘Bragg‑peak’ scatter markers with adaptive labelling in inspector view

In the inspector plot of plopp package, when visualising a 3D object such as the single-crystal diffraction data shown below, I would like to have an option to overlay markers indicating the positions of Bragg peaks. These peaks could be provided as a list of three coordinates with optional labels.

The desired behaviour is the following:

• When the number of scatter points in the top panel is large, only markers should be shown (similar to the white dots in the example below), without labels.
• When the user zooms into a region and the number of visible points falls below a predefined threshold (e.g., fewer than 10), the labels should automatically appear.
• If multiple Bragg reflections share identical x-y coordinates (e.g., identical gamma and nu values), their labels should be merged into a single combined label. In the example below, this is done for the reflection (5 1 -1) and (10 2 -2).

Additionally, when using the selection tool to display the intensity distribution along the third coordinate, I would like the corresponding labels to appear in the lower panel of the inspector. In the example below, the selected point corresponds to three diffraction peaks, and their labels should be shown in the bottom graph.

This functionality would significantly improve the ability to assess the quality of predicted peak positions relative to experimental single-crystal data.

Start in the plopp inspector view and trace how scatter points, zooming, and the selection tool drive the top and lower panels. Confirm how Bragg-peak coordinates and optional labels can be supplied, then verify that markers, merged labels, adaptive label visibility, and lower-panel labels match the described examples.