fix: clarify pooled output logic in SigLIP2

[sameerajashyam]

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Fixes # (issue)

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Clarified misleading comment in modeling_siglip2.py regarding pooled output token position.
Updated the comment to reflect that the final token may be <pad> or <eos>, consistent with SigLIP2’s training (which does not use attention masks).

• Adjusted the _no_split_modules list to match Hugging Face's modular formatting guidelines.
• Verified consistency using check_modular_conversion.py.
  SigLip2 text pooler output selection #39269

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: siglip2