Data loader tutorials

This umbrella collects the Lean side data tutorials:

• Csv: numeric CSV rows and minibatched regression training;
• Npy: NumPy/PyTorch .npy arrays, metadata inspection, and minibatched regression training;
• Cifar10Images: image-shaped NPY arrays, one-hot labels, train/test split, and CNN training.

The reusable library code is available through TorchLean.Data; these files are concrete tutorial entrypoints that can be read, edited, and run.