Both extract methods now can auto-detect the datatype of both global
and per-atom properties. Callers can still enforce different types
if needed by specifying the now optional dtype argument.
The numpy wrapper now has a new extract_atom function method, which
replace the extract_atom_darray and extract_atom_iarray method and
autodetects both type and size. All parameters can still be forced
to use different values if needed.
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