feat: let Dask use shard-aligned writes when sharding enabled (#54)

When --enable-sharding is True, set align_chunks=False to let Dask
rechunk to shard boundaries instead of chunk boundaries.

Aligns with Dask PRs #12104/#12105 for atomic shard writes.
Prevents partial-shard read-modify-rewrite cycles.

Non-sharded workflows unchanged (align_chunks=True preserved).

Co-authored-by: Emmanuel Mathot <emmanuel.mathot@gmail.com>

Author: wietzesuijker

src/eopf_geozarr/conversion/geozarr.py

@@ -716,14 +716,16 @@ def create_geozarr_compliant_multiscales(
 
         # Write the overview dataset
         overview_group = f"{group_name}/{level}"
+        # When sharding enabled, let Dask rechunk to shard boundaries
+        align_chunks_flag = False if enable_sharding else True
         overview_ds.to_zarr(
             output_path,
             group=overview_group,
             mode="w",
             consolidated=True,
             zarr_format=3,
             encoding=encoding,
-            align_chunks=True,
+            align_chunks=align_chunks_flag,
             storage_options=storage_options,
         )