[BE] Simplify tests, elaborate testnames in test_optim.py (#101004)
- Deletes unused kwargs
- Make test names more descriptive to remove need of comments. Overall it's better to codify over comment
- Added a test for duplicate params across groups
- Greatly simplified test_empty_grad to discover that the crux of the bug was NOT its emptiness, but rather with multi-dim emptiness.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101004
Approved by: https://github.com/albanD
