HTML-decode URLs in HTML indexes (#2215)
## Summary
If the index lists a URL like
`https://buf.build/gen/python/hashb-foxglove-protocolbuffers-python/hashb_foxglove_protocolbuffers_python-25.3.0.1.20240226043130+465630478360-py3-none-any.whl`,
we need to decode that to
`https://buf.build/gen/python/hashb-foxglove-protocolbuffers-python/hashb_foxglove_protocolbuffers_python-25.3.0.1.20240226043130+465630478360-py3-none-any.whl`.
Closes https://github.com/astral-sh/uv/issues/2202.
