How to read XDMF in notebook?

Hi all,

I couldn't get to read XDMF files in a notebook

```python
from itkwidgets import view
import vtk
filename='task7/mesh_domains.xdmf'
reader = vtk.vtkXdmfReader()
reader.SetFileName(filename)
reader.Update()
vtk_image = reader.GetOutput()

view(vtk_image)
```

It just produces a black screen:


The XDMF file I'm trying to read can be found [here](https://github.com/RemDelaporteMathurin/FESTIM-workshop/blob/main/tasks/task7/mesh_domains.xdmf).

Is it possible to read XDMF files?

Start by reproducing the provided Python notebook snippet with the linked task7/mesh_domains.xdmf file and inspect the resulting black view. No repository files or tests are named; done means establishing whether this XDMF input can be rendered and documenting a supported notebook path or a clear limitation.

Scritto dal modello di indicizzazione a partire dal testo della issue.