Add debug logging for remote iterator

[aireenmei]

Description

Add debug logging to help with scale testing b/511164291

Tests

Run with these logging on 2xv5e-32 log

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 8.33333% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...rc/maxtext/input_pipeline/multihost_dataloading.py	8.33%	11 Missing ⚠️

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