Add custom `ResponseFormat` support in CallModelInputFilter callback

[sandsc]

call_model_input_filter of RunConfig is invoked immediately before calling the model which allows you to edit the input sent to the model, Is there any change to add response_format: ResponseFormat | None field to support modify response format before calling the model.

[norika1207-lab]

One practical way to make this easier to evaluate is to turn the report into a small contract test around the runtime boundary, not only the user-facing symptom.

For custom ResponseFormat support in CallModelInputFilter, I would check three things: first, the failing input is preserved as a minimal fixture; second, the SDK emits the same observable event/result shape before and after the fix except for the intended change; third, the trace or serialized session contains enough metadata to explain what happened after a resume or retry.

The part that matters for agent systems is durability: if a tool call, memory write, handoff, or structured-output step fails, downstream code should not have to infer state from natural-language output. A focused regression test around that boundary would make the issue much easier to close with confidence.