Fix HF token validation to support Hugging Face CLI cache

[copybara-service]

Fix HF token validation to support Hugging Face CLI cache

This CL ports changes from GitHub PR #4313 (CL 941206211) and adds the necessary Google3 BUILD dependency and visibility updates.

• Fallback to huggingface_hub.get_token() if config.hf_access_token is missing.
• Pass the fallback token to the checkpoint conversion subprocess.
• Add unit tests to verify authentication behavior.
• Add huggingface_hub dependency to maxtext:model_creation_utils.
• Add maxtext to friends package group in huggingface_hub visibility.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/maxtext/utils/model_creation_utils.py	83.33%	0 Missing and 1 partial ⚠️

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