write_h5ed cannot write the output of io.omop.setup_obs

[Zethson]

ed.io.omop.setup_obs returns an object that ed.io.write_h5ed refuses to write, so the OMOP path has no working round trip.

Two independent causes: datetime64 columns (birth_datetime, observation_period_start_date, observation_period_end_date, plus valid_start_date/valid_end_date in var when enrich_var_with_feature_info=True), which anndata has no HDF5 writer for; and all-null object columns (location_id, provider_id, care_site_id are empty in GiBleed), which h5py rejects with TypeError: Can't implicitly convert non-string objects to strings once the datetimes are cast away.

import duckdb, ehrdata as ed

con = duckdb.connect()
ed.dt.gibleed_omop(backend_handle=con)
edata = ed.io.omop.setup_obs(backend_handle=con, observation_table="person_observation_period")
ed.io.write_h5ed(edata, "mre.h5ed")
# IORegistryError: No method registered for writing
# <class 'pandas.core.arrays.datetimes.DatetimeArray'> into <class 'h5py._hl.group.Group'>
# Error raised while writing key 'birth_datetime' of <class 'h5py._hl.group.Group'> to /obs

ehrdata 0.4.0, anndata 0.13.3.post0, h5py 3.16.0, python 3.14.7.