Cannot write a 0 dimensional array with sharding

[d-v-b]

This:

#!/usr/bin/env python3
# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "zarr @ git+https://github.com/zarr-developers/zarr-python.git@main",
# ]
# ///

import zarr

arr = zarr.create_array({}, shape=(), dtype="f4", chunks=(), shards=())
arr[()] = 42.0

Makes this:

(dedl-cube-io) d-v-b@pc ➜  data-model-1 git:(feat/healpix-cli) ✗ uv run zarr_scalar_sharding_bug.py
Traceback (most recent call last):
  File "/home/d-v-b/dev/data-model-1/zarr_scalar_sharding_bug.py", line 13, in <module>
    arr[()] = 42.0
    ~~~^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/array.py", line 2928, in __setitem__
    self.set_basic_selection(cast("BasicSelection", pure_selection), value, fields=fields)
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/array.py", line 3162, in set_basic_selection
    sync(self.async_array._set_selection(indexer, value, fields=fields, prototype=prototype))
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/sync.py", line 159, in sync
    raise return_result
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/sync.py", line 119, in _runner
    return await coro
           ^^^^^^^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/array.py", line 1714, in _set_selection
    return await _set_selection(
           ^^^^^^^^^^^^^^^^^^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/array.py", line 5913, in _set_selection
    await codec_pipeline.write(
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/codec_pipeline.py", line 488, in write
    await concurrent_map(
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/common.py", line 117, in concurrent_map
    return await asyncio.gather(*[asyncio.ensure_future(run(item)) for item in items])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/common.py", line 115, in run
    return await func(*item)
           ^^^^^^^^^^^^^^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/codec_pipeline.py", line 347, in write_batch
    await self.encode_partial_batch(
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/codec_pipeline.py", line 247, in encode_partial_batch
    await self.array_bytes_codec.encode_partial(batch_info)
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/abc/codec.py", line 283, in encode_partial
    await concurrent_map(
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/common.py", line 117, in concurrent_map
    return await asyncio.gather(*[asyncio.ensure_future(run(item)) for item in items])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/core/common.py", line 115, in run
    return await func(*item)
           ^^^^^^^^^^^^^^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/codecs/sharding.py", line 584, in _encode_partial_single
    shard_dict = shard_reader.to_dict_vectorized(np.asarray(_morton_order(chunks_per_shard)))
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/codecs/sharding.py", line 284, in to_dict_vectorized
    starts, ends, valid = self.index.get_chunk_slices_vectorized(chunk_coords_array)
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/d-v-b/.cache/uv/environments-v2/zarr-scalar-sharding-bug-4174d1dad5099f58/lib/python3.12/site-packages/zarr/codecs/sharding.py", line 177, in get_chunk_slices_vectorized
    starts = offsets_and_lengths[:, 0]
             ~~~~~~~~~~~~~~~~~~~^^^^^^
IndexError: too many indices for array: array is 1-dimensional, but 2 were indexed

seems like we are missing some 0D arrays in our sharding test matrix.