Using serde (serde_pyo3) to get __str__ and __repr__ easily.

[Narsil]

Dummy implementation everywhere, but it's a showcase.

[HuggingFaceDocBuilderDev]

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[ArthurZucker]

Fu**ng amazing 🚀 Instead of deriving at compile time a display function for each and every single class in rust, we just rely on the already derived Serialize trait, which give obj.serialize(). so smart, really thanks for finding a much more elegant solution thant #1542