Add shards to valid_encodings to enable sharded Zarr writing

[jacobbieker]

Adds shards to the list of valid_encodings in the zarr backend, so that sharded Zarr V3s can be written.

• Closes Unable to write to sharded Zarr V3 because shards not in valid_encodings #9947

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[jhamman]

Thanks @jacobbieker for opening a PR. Do you have time to add a roundtrip test for this? This test would be a good test to emulate:

xarray/xarray/tests/test_backends.py

Lines 2486 to 2494 in 6bea715

	def test_chunk_encoding(self) -> None:
	# These datasets have no dask chunks. All chunking specified in
	# encoding
	data = create_test_data()
	chunks = (5, 5)
	data["var2"].encoding.update({"chunks": chunks})
	with self.roundtrip(data) as actual:
	assert chunks == actual["var2"].encoding["chunks"]

[jacobbieker]

Thanks @jacobbieker for opening a PR. Do you have time to add a roundtrip test for this? This test would be a good test to emulate:

xarray/xarray/tests/test_backends.py

Lines 2486 to 2494 in 6bea715

	def test_chunk_encoding(self) -> None:
	# These datasets have no dask chunks. All chunking specified in
	# encoding
	data = create_test_data()
	chunks = (5, 5)
	data["var2"].encoding.update({"chunks": chunks})
	with self.roundtrip(data) as actual:
	assert chunks == actual["var2"].encoding["chunks"]

Yep! I think I've added one that works for that, and updated the Zarr V3 loading to include the shards. It seems to pass the tests locally so far at least.

Edit: Ah it seems to cause some issues with threads on 3.12 potentially?