BlockMeanHash constructor
      
      BlockMeanHash({ 
    
    
- int mode = BLOCK_MEAN_HASH_MODE_0,
Implementation
factory BlockMeanHash({int mode = BLOCK_MEAN_HASH_MODE_0}) {
  final p = calloc<cvg.BlockMeanHash>();
  cvRun(() => ccontrib.cv_img_hash_BlockMeanHash_create(mode, p, ffi.nullptr));
  return BlockMeanHash._(p, mode);
}