fix/shard iteration redux

[d-v-b]

Completes the work of #3299 by replacing a second invocation of _iter_chunk_coords with _iter_shard_coords.

In a separate PR, we need to refactor this code block:

zarr-python/src/zarr/core/array.py

Lines 4402 to 4428 in b8dbf56

	if write_data:
	if isinstance(data, Array):
	async def _copy_array_region(
	chunk_coords: tuple[int, ...] | slice, _data: Array
	) -> None:
	arr = await _data._async_array.getitem(chunk_coords)
	await result.setitem(chunk_coords, arr)
	# Stream data from the source array to the new array
	await concurrent_map(
	[(region, data) for region in result._iter_shard_regions()],
	_copy_array_region,
	zarr.core.config.config.get("async.concurrency"),
	)
	else:
	async def _copy_arraylike_region(chunk_coords: slice, _data: NDArrayLike) -> None:
	await result.setitem(chunk_coords, _data[chunk_coords])
	# Stream data from the source array to the new array
	await concurrent_map(
	[(region, data) for region in result._iter_chunk_regions()],
	_copy_arraylike_region,
	zarr.core.config.config.get("async.concurrency"),
	)
	return result

. It's massive code smell to have special "write one array to another" logic defined in the tail end of an array creation function.

I add a test that checks how many get requests we make when calling create_array(data=..). In main, it's 1 get per chunk (bad). In this PR, it's 1 get per shard (better). But we can also get to 0 gets per shard by introducing some special logic for full shard writes. expect this in a later PR.

edit: closes #3169 and #3421

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.92%. Comparing base (3d0e40e) to head (f2c4fac).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3422   +/-   ##
=======================================
  Coverage   94.92%   94.92%           
=======================================
  Files          79       79           
  Lines        9491     9491           
=======================================
  Hits         9009     9009           
  Misses        482      482           

Files with missing lines	Coverage Δ
src/zarr/core/array.py	97.44% <ø> (ø)

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[maxrjones]

Note: we don't actually need one get per shard, but this is the current behavior

Could you open an issue to track this?