[WIP] Upstreaming FSDP2 changes

[SalmanMohammadi]

What does this PR do?

Fixes # (issue)

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[SunMarc]

Hey @SalmanMohammadi, can you explain a bit the changes happening here in the description of the PR ?

[SalmanMohammadi]

Hey @SalmanMohammadi, can you explain a bit the changes happening here in the description of the PR ?

Hey @SunMarc - yes for sure. I had to switch to something else but I'll update this PR and ping for reviews when it's ready.