[playground][ui] fix span parsing of tool result

[axiomofjoy]

{"openinference": {"span": {"kind": "LLM"}}, "input": {"value": "{\"messages\": [{\"role\": \"user\", \"content\": \"What's the weather like in San Francisco?\"}, {\"content\": null, \"refusal\": null, \"role\": \"assistant\", \"tool_calls\": [{\"id\": \"call_y6ds7ub4i6JykGgo5qEDb7oh\", \"function\": {\"arguments\": \"{\\n  \\\"city\\\": \\\"San Francisco\\\"\\n}\", \"name\": \"get_weather\"}, \"type\": \"function\"}]}, {\"content\": \"sunny\", \"role\": \"tool\", \"tool_call_id\": \"call_y6ds7ub4i6JykGgo5qEDb7oh\"}], \"model\": \"gpt-4\"}", "mime_type": "application/json"}, "llm": {"model_name": "gpt-4-0613", "input_messages": [{"message": {"content": "What's the weather like in San Francisco?", "role": "user"}}, {"message": {"role": "assistant", "tool_calls": [{"tool_call": {"function": {"name": "get_weather", "arguments": "{\n  \"city\": \"San Francisco\"\n}"}, "id": "call_y6ds7ub4i6JykGgo5qEDb7oh"}}]}}, {"message": {"tool_call_id": "call_y6ds7ub4i6JykGgo5qEDb7oh", "content": "sunny", "role": "tool"}}], "output_messages": [{"message": {"content": "The weather in San Francisco is sunny.", "role": "assistant"}}], "system": "openai", "invocation_parameters": "{\"model\": \"gpt-4\"}", "provider": "openai", "token_count": {"completion": 8, "prompt": 42, "total": 50}}, "output": {"value": "{\"id\":\"chatcmpl-AViv2UdcUwhyTA8rouadhO2RvRiQf\",\"choices\":[{\"finish_reason\":\"stop\",\"index\":0,\"logprobs\":null,\"message\":{\"content\":\"The weather in San Francisco is sunny.\",\"refusal\":null,\"role\":\"assistant\"}}],\"created\":1732124200,\"model\":\"gpt-4-0613\",\"object\":\"chat.completion\",\"system_fingerprint\":null,\"usage\":{\"completion_tokens\":8,\"prompt_tokens\":42,\"total_tokens\":50,\"completion_tokens_details\":{\"audio_tokens\":0,\"reasoning_tokens\":0,\"accepted_prediction_tokens\":0,\"rejected_prediction_tokens\":0},\"prompt_tokens_details\":{\"audio_tokens\":0,\"cached_tokens\":0}}}", "mime_type": "application/json"}}