Description

Refactors the LoRA parameter restoration utility (restore_lora_from_path) to natively accept and merge parameters of JAX/NNX model wrapper classes.
Standardizing on the NNX state tree representation removes complex state-container unpackings, enhancing trainer safety and maintainability.

Key Changes:

• LoRA Utilities (src/maxtext/utils/lora_utils.py): Overhauled restore_lora_from_path to directly query and merge parameters of NNX wrapper
  classes.
• SFT Trainer (src/maxtext/trainers/post_train/sft/train_sft.py): Simplified parameter setup sequence to cleanly map restored LoRA states
  directly onto the model.

Tests

• Verified via unit testing for LoRA restore functions:

python3 -m pytest tests/post_training/unit/lora_utils_test.py 

Checklist

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• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.