Unused `num_images` param in cifar10 example

The parameter `num_images`  is currently unused in the cifar10 example https://github.com/atong01/conditional-flow-matching/blob/21cd0c888186f6e2b76deb393800361b8a850e9b/examples/cifar10/train_cifar10.py#L52

It would be great to have a `generate_cifar10.py` to generate a given number of images, as in the edm code https://github.com/NVlabs/edm  