Handle circular references in jsonability checks

[CodingFeng101]

Summary

• Treat circular-reference ValueErrors as non-jsonable in is_jsonable()
• Update the serialization regression test to assert the boolean contract instead of expecting the helper to raise

Why

is_jsonable() is a predicate used by serialization helpers to decide whether telemetry payload values can be JSON-encoded. json.dumps() raises ValueError for circular references, so the predicate could raise instead of returning False for a non-jsonable object. Handling this the same way as TypeError and OverflowError keeps the helper fail-safe for unusual agent payloads.

Validation

• .\.venv\Scripts\python.exe -m pytest tests/unit/test_serialization.py -q
• python -m ruff check agentops/helpers/serialization.py tests/unit/test_serialization.py
• python -m ruff format --check agentops/helpers/serialization.py tests/unit/test_serialization.py
• git diff --check