Use checksums for files in file sources

[davelopez]

Is there a chance that we could get the sha-256 checksums for files ? https://huggingface.co/TheBloke/Llama-2-13B-chat-GGML/discussions/10 suggests that this is available somewhere. This would allow caching if we already have the file.

Originally posted by @mvdbeek in #20805 (comment)