[staging] 🐛 Add back per element A-/K-Matrices to result dataset

[s-weigand]

Currently staging saves the combined A-/K-Matrices for all decay elements. If we need those is something to be decided by @ism200 .

However, what we need for validations are data variables on a per-element basis with the following name pattern

• a_matrix_<element_name>
• k_matrix_<element_name>
• k_matrix_reduced_<element_name>

To get rid of the spammy xarray warning:

UserWarning: Duplicate dimension names present: dimensions {'species'} appear more than once in dims=('species', 'species').

Please use ('to_species', 'from_species') notation.

Example outputs

main

staging

[jsnel]

As discussed, please add the suffix at the end. a_matrix_ k_matrix_ rather than a element prefix.

Note element is new name for megacomplexes.

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And in another example: decay_associated_amplitudes_ e.g.: decay_associated_amplitudes_mc1 decay_associated_amplitudes_mc2

A special case is species_associated_amplitudes which we discussed is best to also save with the suffix, which before was only saved at a global level. But with the suffix in place it can then be consolidated later into the global amplitudes (spectra) for plotting purposes (in the extras).