feat(plugin): wrap native session HTTP

[rekram1-node]

Summary

• replace the native session.request mutation hook with session.http around a complete Request -> Response exchange
• expose Effect and standard Promise plugin contracts
• preserve request and response streaming through the native HTTP transport
• migrate the built-in OpenAI hook

The AI SDK path is intentionally unchanged.

Testing

• bun typecheck in packages/ai, packages/core, and packages/plugin
• bun test test/compile.test.ts test/executor.test.ts in packages/ai
• bun test test/plugin/promise.test.ts test/plugin/provider-openai.test.ts test/plugin-hooks.test.ts in packages/core