Move Megatron-FSDP MixedPrecisionPolicy arguments from FSDP adapter t…

[cspades]

…o DDPConfig.

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• Megatron-Bridge prefers all DDP-related arguments (including FSDP) to be included in the DDPConfig. Our adapter allows us to satisfy this requirement.

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• Many triton imports were not guarded and was breaking the CI.

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• Made sure arguments are passed to the DDPConfig correctly (i.e. hasattr(args, f.name) == True), unit tests test the same things.

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[maanug-nv]

why not just add a MixedPrecisionPolicy field instead of duplicating?

[cspades]

Good question! MixedPrecisionPolicy also works without Megatron, i.e. the fully_shard API that native Torch users and NeMo Automodel can use without installing anything. PyPI: https://pypi.org/project/megatron-fsdp/

Nesting that dataclass in the DDPConfig as well as using it as a standalone config can be quite confusing. The only reason I'm even including these arguments into DDPConfig is because of Megatron-Bridge conventions, and prefer not to make it more complicated. One complexity is obvious - that users will need to import Megatron-FSDP sub-modules (megatron_fsdp.MixedPrecisionPolicy) just to use the DDPConfig, not needed and possibly circular.