Also persist asymmetrical units for the MXFP8 transpose weight buffer.

[cspades]

What does this PR do ?

• Needed to support Megatron-native partial CG (where allocated memory needs to be persistent or preserve host-side pointers) with MXFP8 - pass fallback_to_persistent_buffer=self.ddp_config.fsdp_db_use_persist_buf_on_alloc_fail to the MXFP8 transpose weight buffer.
  • This was completely debugged by Codex!

Tested Megatron-native partial CG on this branch: https://github.com/cspades/Megatron-LM/tree/xren/nemotron_fsdp_partcg_mambashard

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[wujingyue]

Still LGTM. Can you add a unit or functional test for this? Someone may accidentally regress this behavior later, and having test coverage would make future PR review less intensive.

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/26213025547