fix(langchain): handle None message id fields

[caroger]

resolves AX issue -https://github.com/Arize-ai/arize/issues/55878
also closes #2426

---

Note

Improve role extraction to handle messages lacking id (e.g., LangGraph streaming, raw dicts) and add tests/cassettes validating agent flows.

• Tracer updates (_tracer.py):
  • Add _infer_role_from_context and _map_class_name_to_role helpers.
  • Rewrite _extract_message_role to use layered strategies: id parsing, type, direct role, and contextual inference (e.g., tool_calls, tool_call_id).
  • Yield MESSAGE_ROLE when derivable; otherwise log a warning instead of asserting.
• Tests:
  • Add tests/test_raw_dict_message.py covering agent invocation with raw dict messages and unit role extraction (including multiple roles).
  • Add VCR cassette tests/cassettes/test_raw_dict_message/test_agent_with_raw_dict_messages.yaml for streaming tool-call and completion flows.

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