Ubench combined testing

[NuojCheng]

Description

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the past.

The rest of the description includes relevant details and context, examples:

• why is this change being made,
• the problem being solved and any relevant context,
• why this is a good solution,
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• shortcomings of the solution and possible future improvements.

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FIXES: b/123456
FIXES: #123456

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BUGS: b/123456

Notice 1: Once all tests pass, the "pull ready" label will automatically be assigned.
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Tests

Please describe how you tested this change, and include any instructions and/or
commands to reproduce.

Checklist

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• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
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• 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.

[codecov]

Codecov Report

❌ Patch coverage is 60.65574% with 48 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/maxtext/trainers/pre_train/train.py	9.09%	4 Missing and 6 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	61.53%	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	83.33%	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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