Support 32 bit in nxs2cbf conversion

[graeme-winter]

Working around issues we fixed elsewhere - but never rolled over to the conversion tool

ws448 x :) $ dxtbx.dlsnxs2cbf /path/to/foo.nxs -o .
Writing images to 008_ZIF8_16-22_x2_001_w001_####.cbf:
  0%|                                             | 0/1750 [00:00<?, ? images/s]
Traceback (most recent call last):
  File "/dls/science/users/gw56/dials-dev/conda_base/bin/dxtbx.dlsnxs2cbf", line 8, in <module>
    sys.exit(run())
  File "/dls/science/users/gw56/dials-dev/modules/dxtbx/src/dxtbx/command_line/dlsnxs2cbf.py", line 73, in run
    dxtbx.util.dlsnxs2cbf.make_cbf(
  File "/dls/science/users/gw56/dials-dev/modules/dxtbx/src/dxtbx/util/dlsnxs2cbf.py", line 188, in make_cbf
    (data,) = dxtbx.nexus.get_raw_data(nxdata, nxdetector, j)
  File "/dls/science/users/gw56/dials-dev/modules/dxtbx/src/dxtbx/nexus/__init__.py", line 580, in get_raw_data
    data_as_flex = _dataset_as_flex(
  File "/dls/science/users/gw56/dials-dev/modules/dxtbx/src/dxtbx/nexus/__init__.py", line 541, in _dataset_as_flex
    raise TypeError(f"Unsupported integer dtype {data_np.dtype}")
TypeError: Unsupported integer dtype uint32

resolved by changes suggested by @noemifrisina