Modify vector field format from .npy to .zarr #21
Description
Going to zarr would allow much better scalability and memory management by using lazy-loading for tractography. At the moment cardiotensor load the entire vector field. The memory limitation can be overcome by using the bin parameter, however for very large high-resolution dataset, heavily binning is not ideal.
Saving as .zarr would also natively have bin version instead of creating them when user request them.