nemotron3 nano recipes

[malay-nagda]

What does this PR do ?

Add Nemotron 3 Nano performance recipes

Changelog

        nemotronh_3_nano_pretrain_config_b200,
        nemotronh_3_nano_pretrain_config_b300,
        nemotronh_3_nano_pretrain_config_gb200,
        nemotronh_3_nano_pretrain_config_gb300,
        nemotronh_3_nano_pretrain_config_h100,

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Additional Information

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Summary by CodeRabbit

• New Features
  • Expanded Nemotron 3 Nano pretraining support across multiple GPU platforms: GB300, GB200, B300, B200, and H100 with optimized configurations for each variant
  • Added mixed-precision training options including BF16 and FP8 precision formats, enabling flexible optimization for performance and memory efficiency based on deployment requirements

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[tomlifu]

LGTM