Fix559 Change reference/access of individual pack in the MultiPack from (array) index based to pack_id based (to facilitate delete, insert), with version-enabled backward compatibility

forte/data/multi_pack.py

@@ -689,10 +689,11 @@ def from_string(cls, data_content: str):
  # can not use explict type hint for mp as pylint does not allow type change
  # from base_pack to multi_pack
  mp = super().from_string(data_content)
- # pylint: disable=no-member
  # (fix 595) change the dictionary's key after deserialization from str back to int
- mp._inverse_pack_ref = {
- int(k): v for k, v in mp._inverse_pack_ref.items()
+ assert isinstance(mp._inverse_pack_ref, Dict)
+ mp._inverse_pack_ref = { # pylint: disable=no-member
+ int(k): v
+ for k, v in mp._inverse_pack_ref.items() # pylint: disable=no-member
  }
 
  return mp