Parse agent traces messages for SFT using teich

[lhoestq]

small breaking change (mostly for the dataset viewer on HF that has to take this into account): the field "traces" is renamed "trace" cc @cfahlgren1

This PR adds the teich extracted traces data, i.e. the fields messages, prompt, tools and metadata

In [1]: from datasets import load_dataset

In [2]: ds = load_dataset("lhoestq/agent-traces-example", split="train")

In [3]: ds[0]["messages"]
[{'role': 'user', 'content': 'Download a random dataset from Hugging Face, use DuckDB to inspect it, and come back with a short report about it. Be concise and include: dataset name, what files/format you found, row count or rough size if you can determine it,...'
 ...]

[HuggingFaceDocBuilderDev]

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