Fix/nnx sharding

[hsuan-lun-chiang]

Description

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[codecov]

Codecov Report

❌ Patch coverage is 51.02041% with 72 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/maxtext/trainers/pre_train/train.py	8.10%	30 Missing and 4 partials ⚠️
src/maxtext/common/checkpointing.py	35.71%	8 Missing and 1 partial ⚠️
src/maxtext/trainers/diloco/diloco.py	75.00%	4 Missing and 4 partials ⚠️
...axtext/trainers/post_train/sft/train_sft_native.py	64.28%	3 Missing and 2 partials ⚠️
src/maxtext/checkpoint_conversion/to_maxtext.py	0.00%	4 Missing ⚠️
src/maxtext/utils/train_utils.py	33.33%	3 Missing and 1 partial ⚠️
src/maxtext/utils/sharding.py	78.57%	1 Missing and 2 partials ⚠️
src/maxtext/layers/nnx_wrappers.py	60.00%	2 Missing ⚠️
...rc/maxtext/utils/generate_param_only_checkpoint.py	80.00%	1 Missing and 1 partial ⚠️
src/maxtext/checkpoint_conversion/utils/utils.py	0.00%	1 Missing ⚠️

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