Fix OpenAPI codegen for binary stream responses

[renardeinside]

Summary

• Fix OpenAPI TypeScript codegen returning res.json() for unknown/binary content types (e.g. application/vnd.apache.arrow.stream, application/vnd.apache.parquet). Previously, vendor-specific binary media types fell through to ResponseContentType::Unknown, which incorrectly called res.json() — failing at runtime on binary data.
• The generated code now returns the raw Response object ({ data: res }) for unrecognized content types, preserving streaming capability via ReadableStream.
• Added a dedicated test (test_response_binary_stream_returns_raw_response) verifying the fix with a vendor binary content type.

Test plan

• New test test_response_binary_stream_returns_raw_response passes
• Full OpenAPI test suite passes (102 tests)
• Verify generated client code works end-to-end with a FastAPI streaming endpoint

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