Conversion scripts fail on standard TPU VMs for large models

### Bug report

The [official instruction]([https://maxtext.readthedocs.io/en/latest/guides/checkpointing_solutions/convert_checkpoint.html#hugging-face-to-maxtext) for model conversion failed on a standard TPU-v5p VM for large models such as QWen3-235B, with CPU OOM errors when sharding MoE layers. Since on GCP the CPU memory is fixed (400GB), I wonder if we can improve the script to bypass this issue, or is the doc outdated?

Also for the model conversion the sharding process with default simulated_cpu_devices_count=16 is very very slow (even for 30B model).

### Logs/Output

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### Environment Information

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### Additional Context

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