[NAdam] Add capturable API and tests + fix differentiable (#106615)
This PR:
- adds a capturable API for NAdam similar to Adam(W)
- adds tests accordingly
- discovered and fixed bugs in the differentiable implementation (now tested through the capturable codepath).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106615
Approved by: https://github.com/albanD
