Function open_sparse_matrix 

pub fn open_sparse_matrix(
    backend_file: &str,
    backend: &SparseIoBackend,
) -> Result<Box<dyn SparseIo<IndexIter = Vec<usize>>>>

Open a sparse matrix io (backend)

• backend_file: file path to the sparse matrix
• backend: backend type (HDF5 or Zarr)