Qwen3 Preprocessing

[eitanporat]

Description

This PR implements the pre-processing required for qwen3 omni it should be merged with @hengtaoguo's PR https://github.com/AI-Hypercomputer/maxtext/pull/2613

Tests

I ran inference successfully!

Checklist

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• [X] I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
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• [X] 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.