[dev] feat(moe): Support packed sequence for gated delta net (GDN)

[yuzhongw-nvidia]

What does this PR do ?

Support packed sequence for gated delta net (GDN).

PR for main: #2645

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flowchart LR
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[yuzhongw-nvidia]

/ok to test ae8806c

[yuzhongw-nvidia]

/ok to test 545a2a5

[kunlunl]

Also need to update this line https://github.com/yuzhongw-nvidia/Megatron-LM/blob/befbcd2a10b60deb4edbd0f758275b26a6df83c7/megatron/core/ssm/gated_delta_net.py#L741 to param = param[tuple(slices)]?

[yuzhongw-nvidia]

Also need to update this line https://github.com/yuzhongw-nvidia/Megatron-LM/blob/befbcd2a10b60deb4edbd0f758275b26a6df83c7/megatron/core/ssm/gated_delta_net.py#L741 to param = param[tuple(slices)]?

Thanks. Resolved.

[kunlunl]

/ok to test 80d2d1c

[yaox12]

LGTM. Please resolve the conflicts.

[yuzhongw-nvidia]

LGTM. Please resolve the conflicts.

Thanks! There are some E2E numerical issues reported by @xiaoyao0115, and we are working on them. Will resolve the conflicts after that.

[Code4Graph]

try the commit [e94395d] to fine-tune qwen3.5-4B with sequence packing and see grad_norm explosion, leading to final accuracy 0.