literal_eval on integers

[tkmmark]

This applies to mesh_qad_pseudo.py's data method and any other methods that call literal_eval

consider changing
literal_eval(key)
to
literal_eval(key) if not isinstance(key, int) else key

There is some underlying assumption that dictionary keys of mesh elements will necessarily be strings in many of compas_singular's methods
Perhaps this is because of the way datastructures are serialised in earlier versions of COMPAS, which stringify all keys as json.dump tends to do...
However, this causes issues when the keys are already integers.