Python: fix circular reference error in KernelArguments.dumps() during OTel diagnostics

[MaxwellCalkin]

Motivation and Context

Fixes #13393

When running Process Framework steps with SEMANTICKERNEL_EXPERIMENTAL_GENAI_ENABLE_OTEL_DIAGNOSTICS_SENSITIVE=true, every function invocation fails with Circular reference detected. This happens because:

1. KernelFunction.invoke() calls arguments.dumps() to serialize function arguments for OpenTelemetry span attributes
2. Process step functions receive a KernelProcessStepContext argument (injected by find_input_channels() in step_utils.py)
3. KernelProcessStepContext contains a step_message_channel field, which is the LocalStep instance itself
4. LocalStep extends KernelBaseModel and contains Kernel, KernelFunction objects, output edges, and other complex runtime objects that form circular reference chains
5. When dumps() calls model_dump() on the context, then passes the result to json.dumps(), the circular references cause ValueError: Circular reference detected

Description

Makes KernelArguments.dumps() resilient to circular references:

• Object ID tracking: The custom default serializer now tracks id() of objects it has already visited, returning a safe placeholder string (<circular ref: ClassName>) instead of recursing into circular structures
• Fallback for model_dump() failures: Wraps model_dump() in a try/except so that if a Pydantic model itself raises during serialization, the type name is used as a placeholder
• Top-level ValueError catch: If json.dumps() still detects a circular reference (e.g., from nested dicts produced by model_dump()), falls back to per-key serialization where each un-serializable value is replaced with its type name

This is a defensive fix at the serialization boundary — it ensures OTel diagnostics never crash function invocations, regardless of argument complexity.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass
• New unit tests added for circular reference handling in test_kernel_arguments.py

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Disclosure: This PR was authored by Claude Opus 4.6 (an AI). I'm applying for a role at Microsoft — see maxwellcalkin.com for background.