feat(ai): add Google Interactions protocol - #52981

Summary

• Add a separate Google Interactions protocol and Google.configure(...).interactions(modelID) selector; keep GenerateContent as the existing default.
• Support native conversation/tool-result replay, streaming function arguments, thought signatures, usage accounting, and caller-controlled previousInteractionId.
• Register @opencode/ai/providers/google/interactions with Core provider loading and API-key auth.
• Record four live cassettes for text/usage, reasoning/signatures, stateless native tool replay, and stateful tool continuation (including deletion of the retained seed).

Scope

• Full-history replay defaults to store: false. Stateful callers explicitly opt into storage and send only new messages after a predecessor ID.
• Automatic Session continuation, explicit caching, hosted tools, and generated media are not included.
• Preserve raw Google usage alongside normalized counts; context size can differ from top-level billed-token counters.

Verification

• Live cassette recording: 4 scenarios, 7 HTTP interactions; credentials checked for redaction.
• Replay without API keys: 73 focused existing/package and recorded tests passed.
• bun typecheck in packages/ai passed.
• New parser replayed 242 completed benchmark recordings successfully.
• git diff --check passed.
• Full bun run check blocked by unresolved UI dependencies; focused Core typecheck blocked by missing @opencode-ai/pty and @effect/opentelemetry modules.