More precise dataset size computation
Currently, the Hub uses the `/size` endpoint's `num_bytes_original_files` value to display the `Size of downloaded dataset files` on a dataset's card page. However, this value does not consider a possible overlap between the configs' data files (and simply [sums](https://github.com/huggingface/datasets-server/blob/e4aac49c4d3c245cb3c0e48695b7d24a934a8377/services/worker/src/worker/job_runners/dataset/size.py#L97-L98) all the configs' sizes up), in which case the shared files need to be downloaded only once. Both `datasets` and `hfh` recognize this (by downloading them once), so the size computation should account for it, too.

cc @guipenedo who reported this behavior first
More precise dataset size computation: Currently, the Hub uses the `/size` endpoint's `num_bytes_original_files` value to display the `Size of downloaded dataset files` on a dataset's card page. However, this value does not consider a possible overlap between the configs' data files (and simply [sums](https://github.com/huggingface/datasets-server/blob/e4aac49c4d3c245cb3c0e48695b7d24a934a8377/services/worker/src/worker/job_runners/dataset/size.py#L97-L98) all the configs' sizes up), in which case the shared files need to be downloaded only once. Both `datasets` and `hfh` recognize this (by downloading them once), so the size computation should account for it, too.

cc @guipenedo who reported this behavior first