docs: def is_valid_chunksize(chunk_size):
          """Check if size is valid."""
          min_csize = current_app.config['FILES_REST_MULTIPART_CHUNKSIZE_MIN']
          max_csize = current_app.config['FILES_REST_MULTIPART_CHUNKSIZE_MAX']
          return chunk_size >= min_csize and chunk_size <= max_csize