Gemma model verifications

[jlarson4]

Description

Additional Gemma 4 verifications requested by @UriKialy. Verified 3 new models including google/gemma-4-31B, re-ran stale verification of others.

Related to #1447

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• 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 not rewritten tests relating to key interfaces which would affect backward compatibility