Set lazy_load_tensors to true by default.

[niting]

Description

Lazy loading tensors saves on disk space and the path has now been optimized to be quicker with caching. Added appropriate documentation to indicate that this does not work for models with multimodal capabilities.

Tests

Ran checkpoint conversion test.

Checklist

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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 0% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/maxtext/checkpoint_conversion/to_maxtext.py	0.00%	1 Missing ⚠️

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