Add arrow data storage support for linfa pre-processing and training module about linfa HOT 3 OPEN

I don't want to abandon ndarray completely, since all the downstream code relies on it. If we add arrow support then we should support both, preferably via a generic trait that abstracts over the underlying data format. Unfortunately integration between ndarry and arrow doesn't yet exist directly, but they did talk about it here

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That makes sense totally. Just to add support for arrow without abandoning ndarray. Thanks

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I have done further investigation and it looks like you must have ndarray or array-like data structure support alongside. Because there are file types like images, and texts that can not be loaded as data frames, which needed to be loaded one by one or as a batch in an array/tensor for further training, the way datasets in pytorch.utils do.

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