[adam] Add not torch.jit.is_scripting() as a requirement for switching to fused (#92181)
A "fix" following https://github.com/pytorch/pytorch/pull/90865. Realized that fused is not compatible with torch.jit.is_scripting() when looking at a later line.
Took the opportunity to make the code cleaner/slightly more performant (with the extends) as well.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92181
Approved by: https://github.com/albanD
