Lazy import `packaging` in `torch_version` (#71345)
Summary:
As it is a pretty big package and to be used during normal
course of PyTorch initialization
Fixes https://github.com/pytorch/pytorch/issues/71280
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71345
Reviewed By: seemethere
Differential Revision: D33594547
Pulled By: malfet
fbshipit-source-id: e0abea82dbdc29914512b610692701140d3e68a2
(cherry picked from commit 1ff7f65cc1ad499a71457368894ca14bed069749)
