fix: add missing all-gather for nnx vocabulary tiling

[mesakhcienet]

Description

Add missing all-gather of nnx embedding table. Allow the NNX memory and performance simiilar to Linen version.

Tests

Script : tpu-recipe for gemma4-2b

Machine : Cluster of ironwood v7x

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• 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

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!