[PyTorch] Replaced deprecated `pkg_resources` with `packaging`

[denera]

Description

pkg_resources has been deprecated a while ago, and the deprecation warning turned into an error with a recent setuptools update. This PR replaces pkg_resources.packaging.Version in pytorch/attention.py with packaging.version.Version and adds packaging as an install dependency in `setup.py.

Type of change

• [ ] Documentation change (change only to the documentation, either a fix or a new content)
• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Changes

• Replace pkg_sources.packaging.Version with packaging.version.Version in pytorch/attention.py.
• Add packaging as an install dependency in setup.py.

Checklist:

• [x] I have read and followed the contributing guidelines
• [x] The functionality is complete
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes