fix(models): register gemma 4 model names

[pandego]

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: Gemma 4 not registered in LLMRegistry — Gemma.supported_models() only matches gemma-3.* #5156
• Related: N/A

2. Or, if no issue exists, describe the change:

Problem:
LLMRegistry only matched gemma-3.*, so string model names like gemma-4-31b-it were rejected even though the underlying Gemini-backed Gemma path already supports them.

Solution:
Broaden Gemma.supported_models() to match the full gemma-* family and add a registry regression test covering Gemma 3 plus Gemma 4 model names.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Passed locally:

• uv sync --extra test
• uv run pytest tests/unittests/models/test_models.py tests/unittests/models/test_gemma_llm.py

Manual End-to-End (E2E) Tests:

Not run for this focused registry fix.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

This keeps the fix narrowly scoped to registry matching. It does not change Gemma request handling itself.

[rohityan]

Hi @pandego , Thank you for your contribution! We appreciate you taking the time to submit this pull request. Your PR has been received by the team and is currently under review. We will provide feedback as soon as we have an update to share.

[rohityan]

Hi @pandego , closing this since it has been fixed in this commit (9d4ecbe)