Feat: Support for Structured Output Streaming Strategies

[nikas-belogolov]

Currently, @tanstack/ai provides excellent support for streaming text and handling final structured outputs via Zod schemas. However, for complex UIs (like real-time dashboards or forms being filled by AI), waiting for the entire JSON object to resolve before rendering can feel slow.

I propose adding Streaming Strategies for Structured Outputs. This would allow developers to access "partial" state of a Zod schema as it streams in, similar to how libraries like ai sdk (Vercel) handle it with streamObject.

This could be achieved by Integrating a parser like best-effort-json-parser or incomplete-json-parser.