Implement Zarr Merger

[drbeh]

The main challenge with whole slide images (WSI) is that they do not commonly fit into CPU/GPU memory. Thus requires patching when performing inference. Although our WSIReader efficiently handle loading this patches without loading the entire WSI, the outputs also will be patches that usually cannot be merged on the memory so it requires Mergers that can effectively handle these outputs and merge them on the disk. To that end, Zarr is being used in digital pathology, which is a format for the storage of chunked, compressed, N-dimensional arrays.