Function save_nifti 

pub fn save_nifti(
    data: &[f64],
    dims: (usize, usize, usize),
    voxel_size: (f64, f64, f64),
    affine: &[f64; 16],
) -> Result<Vec<u8>, String>

Save data as NIfTI bytes

Writes an uncompressed .nii file