desi_preproc_darks ragged nested sequences deprecation

[sbailey]

From /global/cfs/cdirs/desi/spectro/redux/daily/run/scripts/night/20260112/pdark-20260112-00331478-a0123456789-47729488.log:

/global/common/software/desi/perlmutter/desiconda/20240425-2.2.0/code/desispec/main/py/desispec/scripts/preproc_darks_mpi.py:193: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray.
  all_data_header_cams = np.array(all_data_header_cams)

At best this is a deprecated feature that will stop working in a future version of numpy. At worst this isn't doing what we intend it to do and it is a bug.

Investigate what all_data_header_cams is prior to wrapping it with np.array(...) and what the intended result is meant to be, and update.