Unescaped config names with special characters in the URL

When playing with mlcroissant, we observed the following issue:

[bigcode/commitpackft](https://huggingface.co/datasets/bigcode/commitpackft) has both the configs `c` and `c#`. When going to https://huggingface.co/api/datasets/bigcode/commitpackft/parquet/c#/train/0.parquet, it lists https://huggingface.co/api/datasets/bigcode/commitpackft/parquet/c/train/0.parquet (instead of https://huggingface.co/api/datasets/bigcode/commitpackft/parquet/c%23/train/0.parquet).

Should dataset names / config names be escaped in the URLs?

cc @severo @lhoestq

Reproduce the issue with the dataset-viewer API URL for the c# configuration, then trace the endpoint that constructs the parquet URL. Verify that dataset and configuration names with special characters are URL-escaped, and confirm the response uses c%23 rather than c in the generated link.

Written by the indexing model from the issue text.