OpenRouter Anthropic model doesn't support structured output

[riywo]

[2025-05-09 17:46:15.797 -0700] INFO: Test result: FAIL, Summary:
Error: Failed to parse. Text: "". Error: SyntaxError: Unexpected end of JSON input

Troubleshooting URL: https://js.langchain.com/docs/troubleshooting/errors/OUTPUT_PARSING_FAILURE/

[2025-05-09 17:46:15.799 -0700] INFO: LLM usage: OpenRouter/anthropic/claude-3.7-sonnet ($0.18955) Total input: $0.18289/60,964tk output: $0.00666/444tk cachedRead: $0.00000/0tk cachedWrite: $0.00000/0tk

Because response_format isn't supported: https://openrouter.ai/models?fmt=cards&supported_parameters=response_format&arch=Claude

So, we must fail earlier if Anthropic models are specified on OPENROUTER_MODEL.

When selecting a model, we should hit this API and check the capabilities: https://openrouter.ai/docs/api-reference/list-endpoints-for-a-model

Note: Directly using Anthropic models i.e. ANTRHOPIC_MODEL is fine. This is only an issue with OpenRouter and Anthropic.