[use cases] use logfire + pne to trace the prompt

[Undertone0809]

🚀 Feature Request

Logfire is an observability platform built on the same belief as our open source library — that the most powerful tools can be easy to use.

We can use logfire to do some trace activity like LangSmith. So add a use cases to show how to use logfire to trace prompt. I hope to add logfire into a Agent use cases to show how to integration application.

Link: https://docs.pydantic.dev/logfire/