Refactor ZenFlow integration in AdamW optimizers.
- Updated the DeepSpeedEngine to ensure ZenFlow manages the backward pass, allowing for selective parameter updates and synchronization boundaries.
- Replaced direct calls to `torch._utils.is_compiling()` with `is_compiling()` from the compiler module for better clarity and maintainability.
Signed-off-by: Tingfeng Lan <erc8gx@virginia.edu>
Co-authored-by: Yusen Wu <xrn4ub@virginia.edu>
