feat(claude): add structured output support

[marwan38]

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feat: claude structured json output

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[marwan38]

I was hesitant on providing a wrapper for ResponseFormat, but this is consistent in how all the other models define it.

[marwan38]

I wasn't sure if example > readme.
I found the readme helpful on the documentation website when I initially started using eino.
examples/ are better for more complex use cases, and I don't think this is one.

[vika2603]

I need this feature. Thank you

[marwan38]

Sorry, not sure who I can tag @hi-pender.
I don't want this to go stale.

[marwan38]

Seems like Anthropics structured output API does not work like I expected.

During agentic runs (ReAct), claude would ALWAYS short circuit and stop with reason: end_turn and set a placeholder output. Perhaps my ignorance in LLM, or rather the mess of it, made me expect something but get another.

or perhaps there's something wrong on my end..