What options do I have for `<U#` type data saving in zarr?

What is your issue?

So I tried out xarray today with zarr version 3.0.4, and encountered these scary warnings:

/nix/store/qasysgiacqplrbda5yl65wg7jrs0gcjl-python3-3.12.9-env/lib/python3.12/site-packages/zarr/codecs/vlen_utf8.py:44: UserWarning: The codec `vlen-utf8` is currently not part in the Zarr format 3 specification. It may not be supported by other zarr implementations and may change in the future.
  return cls(**configuration_parsed)
/nix/store/qasysgiacqplrbda5yl65wg7jrs0gcjl-python3-3.12.9-env/lib/python3.12/site-packages/zarr/core/array.py:3991: UserWarning: The dtype `<U5` is currently not part in the Zarr format 3 specification. It may not be supported by other zarr implementations and may change in the future.
  meta = AsyncArray._create_metadata_v3(
/nix/store/qasysgiacqplrbda5yl65wg7jrs0gcjl-python3-3.12.9-env/lib/python3.12/site-packages/zarr/api/asynchronous.py:203: UserWarning: Consolidated metadata is currently not part in the Zarr format 3 specification. It may not be supported by other zarr implementations and may change in the future.
  warnings.warn(

A MWE is:

import xarray as xr
import numpy as np

xr.DataArray(np.array([
    "hello",
    "world",
])).to_zarr("test_utf8_strings.zarr")

Is <U5 a variable length utf8 type? It shouldn't be... Also, what are my alternatives?

Start with the supplied xarray and NumPy reproducer and the warnings from zarr's vlen_utf8.py and array.py. Compare the reported <U5 and vlen-utf8 behavior with the Zarr format 3 specification and identify the supported string-saving alternatives. Done means the available options and compatibility implications are clearly documented.