z-index is not imported or exported with GeoJSONs

[BPdeRooij]

Describe the bug
The z-index is not taken into account when importing or exporting annotations with GeoJSON.

To Reproduce
Create a WsiAnnotations object containing annotations with z-indices. Calling WsiAnnotations.as_geojson() fails to export z-index of the annotations. When importing annotations with WsiAnnotations.from_geojson(), z-index is also ignored.

Expected behavior
WsiAnnotations.as_geojson, WsiAnnotations.from_geojson and _geometry_to_geojson should all be able to handle annotations with z-indices correctly.

Environment
dlup version: 0.5.1
How installed: installed from main branch
Python version: 3.10
Operating System: Linux

Additional context
A working fix can be found in this branch.

[jonasteuwen]

I don't think it's an issue as the export should export it without needing to sort again, the output itself is already sorted, in the GeoJSON order. There is a test that checks if reading back gives the same result

[BPdeRooij]

The annotations are outputted in the correct order, but information is lost in the process. Including the z-index in the GeoJSON properties when exporting (or importing) would not break GeoJSON conventions and would ensure that all information is preserved. I believe it would be useful to include the z-index for completeness and reproducibility.