Add support for Gemini 3.0 models

[iany0]

This PR adds support for Gemini 3.0 Flash and Pro models.

[iany0]

/gcbrun exp -n wq -m vertex_ai_gemini-3-pro-chat -b quick-test -ns 1 -ll global -ag

[github-actions]

Requested GKE Job: ofg-pr-1219-wq

JOB: https://console.cloud.google.com/kubernetes/job/us-central1-c/llm-experiment/default/ofg-pr-1219-wq
REPORT: https://llm-exp.oss-fuzz.com/Result-reports/ofg-pr/2026-01-24-1219-wq-quick-test/index.html
BUCKET: https://console.cloud.google.com/storage/browser/oss-fuzz-gcb-experiment-run-logs/Result-reports/ofg-pr/2026-01-24-1219-wq-quick-test
BUCKET (GS): gs://oss-fuzz-gcb-experiment-run-logs/Result-reports/ofg-pr/2026-01-24-1219-wq-quick-test

[iany0]

/gcbrun exp -n wq -m vertex_ai_gemini-3-flash-chat -b quick-test -ns 1 -ll global -ag

[github-actions]

Requested GKE Job: ofg-pr-1219-wq

JOB: https://console.cloud.google.com/kubernetes/job/us-central1-c/llm-experiment/default/ofg-pr-1219-wq
REPORT: https://llm-exp.oss-fuzz.com/Result-reports/ofg-pr/2026-01-25-1219-wq-quick-test/index.html
BUCKET: https://console.cloud.google.com/storage/browser/oss-fuzz-gcb-experiment-run-logs/Result-reports/ofg-pr/2026-01-25-1219-wq-quick-test
BUCKET (GS): gs://oss-fuzz-gcb-experiment-run-logs/Result-reports/ofg-pr/2026-01-25-1219-wq-quick-test