support stress reading in Voigt format

[sandipde]

metatrain/src/metatrain/utils/data/readers/ase.py

Line 211 in 08ec341

if values.shape == (9,):

It would be great to add the support to read the stress in voigt format as well if the array is found to be of len 6.

[pfebrer]

Hmm I see the problem, I imagine you have a big dataset with stress written like this? But I imagine one could argue why reading those 6 numbers as Voigt notation instead of some other decomposition, e.g. one l=0 and one l=2 tensor 😅

Is it a big problem to rewrite the dataset with 9 values?