fix: change MovieLens download URLs from https to http

[qtuantruong]

Description

HTTPS requests to files.grouplens.org fail with a "This connection is not private" error due to an invalid/expired SSL certificate. Since our download utility can fetch data directly over HTTP without issue, this PR switches the four MovieLens download URLs (100K, 1M, 10M, 20M) from HTTPS to HTTP.

Related Issues

Checklist:

• I have added tests.
• I have updated the documentation accordingly.
• I have updated README.md (if you are adding a new model).
• I have updated examples/README.md (if you are adding a new example).
• I have updated datasets/README.md (if you are adding a new dataset).

[hieuddo]

I think changing from https to http won't fix the issue. The server redirects http requests back to https:

~ curl -ILs "http://files.grouplens.org/datasets/movielens/ml-100k/u.data"
HTTP/1.1 301 Moved Permanently
Date: Sun, 13 Sep 2026 09:21:54 GMT
Server: Apache
Location: https://files.grouplens.org/datasets/movielens/ml-100k/u.data
Content-Type: text/html; charset=iso-8859-1

And on HTTPS, their SSL certificate expired on 28 Aug 2026:

~ echo | openssl s_client -servername files.grouplens.org -connect files.grouplens.org:443 2>/dev/null | openssl x509 -noout -dates

notBefore=Aug 28 00:00:00 2025 GMT
notAfter=Aug 28 23:59:59 2026 GMT

Hopefully they'll renew the SSL certificate soon, and the original URLs will work again.