Add metadata to dtype when kind is 'O'

[magland]

In order to get pynwb validation to pass I needed to make the tweak of this PR. It seems that h5py uses a vlen field in metadata for a numpy dtype, and pynwb inspects that. I don't understand exactly what this is about. But when I set it to bytes in this case, the validation passes.

Here's a test validation script where things are passing with this PR

import pynwb
from pynwb import CORE_NAMESPACE
from pynwb.validate import ValidatorMap
import h5py
import remfile
import lindi


def test_validate(io: pynwb.NWBHDF5IO):
    namespace = CORE_NAMESPACE
    validator = ValidatorMap(namespace=io.manager.namespace_catalog.get_namespace(name=namespace))
    builder = io.read_builder()
    validation_errors = validator.validate(builder=builder)
    if len(validation_errors) == 0:
        print('Validation passed!')
    else:
        print('Validation failed!')
        for ve in validation_errors:
            print(ve)


if __name__ == "__main__":
    # https://neurosift.app/?p=/nwb&dandisetId=000409&dandisetVersion=draft&url=https://api.dandiarchive.org/api/assets/c04f6b30-82bf-40e1-9210-34f0bcd8be24/download/

    print('')
    print('Validating with HDF5 URL...')
    h5_url = 'https://api.dandiarchive.org/api/assets/c04f6b30-82bf-40e1-9210-34f0bcd8be24/download/'
    remf = remfile.File(h5_url)
    h5f = h5py.File(remf, mode='r')
    with pynwb.NWBHDF5IO(file=h5f, mode='r', load_namespaces=True) as io:
        test_validate(io)

    print('')
    print('Validating with LINDI URL...')
    lindi_url = 'https://lindi.neurosift.org/dandi/dandisets/000409/assets/c04f6b30-82bf-40e1-9210-34f0bcd8be24/zarr.json'
    ff = lindi.LindiH5pyFile.from_reference_file_system(lindi_url)
    with pynwb.NWBHDF5IO(file=ff, mode='r', load_namespaces=True) as io:
        test_validate(io)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.34%. Comparing base (3c4562f) to head (d269450).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #47   +/-   ##
=======================================
  Coverage   82.33%   82.34%           
=======================================
  Files          28       28           
  Lines        1970     1971    +1     
=======================================
+ Hits         1622     1623    +1     
  Misses        348      348           

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[rly]

Looks good. Let's try to validate all NWB files on DANDI and see if this will work. We should look more closely into why the logic is what it is in PyNWB...