fix(google): serialize Veo image inputs as bytesBase64Encoded

[f0rr0]

Summary

• serialize Veo image-to-video inputs as bytesBase64Encoded instead of inlineData
• serialize referenceImages[].bytesBase64Encoded the same way
• update the Google video model tests to assert the request body shape

Why

Google Veo image-to-video requests against the Gemini predictLongRunning endpoint fail when the image is sent as inlineData. The current provider emits inlineData for both options.image and referenceImages, which causes first-frame video generation to fail in real usage.

Validation

• pnpm --filter @ai-sdk/google exec vitest --config vitest.node.config.js --run src/google-generative-ai-video-model.test.ts
• pnpm --filter @ai-sdk/google type-check
• validated the same serializer change locally against @ai-sdk/google@3.0.53 through both google.video(...).doGenerate(...) and the full experimental_generateVideo(...) path