code: def pack_vec(
      self, vec: torch.LongTensor, num_shift_bit, num_elem_each_pack
  ) -> FV:
      return self.coder.pack_u64_vec(
          vec.detach().tolist(), num_shift_bit, num_elem_each_pack
      )
  
imports: from typing import List, Optional, Tuple
  import torch
  from fate_utils.ou import CiphertextVector, PlaintextVector
  from fate_utils.ou import Coder
  from fate_utils.ou import Evaluator
  from fate_utils.ou import PK
  from fate_utils.ou import SK
  from fate_utils.ou import keygen
  from .type import TensorEvaluator
label_desc: Use image node_id 4 for calling the Coder obj's underlying member method code with example usage: obj.pack_vec(vec, num_shift_bit, num_elem_each_pack) and returns: self