Adds support for RectilinearChunkGrid, enabling arrays with variable chunk sizes along each dimension in Zarr v3. Users can now specify irregular chunking patterns using nested sequences: chunks=[[10, 20, 30], [25, 25, 25, 25]] creates an array with 3 chunks of sizes 10, 20, and 30 along the first dimension, and 4 chunks of size 25 along the second dimension. This feature is useful for data with non-uniform structure or when aligning chunks with existing data partitions. Note that RectilinearChunkGrid is only supported in Zarr format 3 and cannot be used with sharding or when creating arrays from existing data via from_array().