Add Palm2 API support in JS SDK

[duongynhi000005-oss]

/claim #279\n\nAdds Palm2AI support, unit tests under src/tests/palm2, and a runnable chat-with-palm2 jsonnet example.\n\nValidation:\n- npm run build\n- npx vitest run src/tests/palm2/palm2.test.ts\n- npm install && timeout 20s npm run start (example smoke)

[github-actions]

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[duongynhi000005-oss]

I have read the Arakoo CLA Document and I hereby sign the CLA