[refactor] engines: use datetime.fromisoformat instead of datetime.strptime where possible (#6394)

Refactor engines that parse ISO 8601 dates with strptime to use
fromisoformat instead. In most cases this is a direct replacement of
strptime(text, "format") with fromisoformat(text).

For engines where the source has a trailing "Z" that strptime consumed
as a literal (e.g. "%Y-%m-%dT%H:%M:%S.%fZ" in huggingface.py), add
rstrip("Z") to keep the output naive and preserve the existing behavior.

In sogou.py the date is extracted with a regular expression, which can
yield strings like "2026-7-11". strptime accepts this via its format
string, but fromisoformat does not. To preserve the existing behavior
and satisfy the format fromisoformat expects, add zero-padding for the
month and day.

Closes: #6098
---------
Signed-off-by: OneVth <onebrotravel@gmail.com>

searx/engines/bitchute.py

@@ -44,7 +44,7 @@ def response(resp):
                 "url": 'https://www.bitchute.com/video/' + item['video_id'],
                 "content": html_to_text(item['description']),
                 "author": item['channel']['channel_name'],
-                "publishedDate": datetime.strptime(item["date_published"], "%Y-%m-%dT%H:%M:%S.%fZ"),
+                "publishedDate": datetime.fromisoformat(item["date_published"].rstrip("Z")),
                 "length": item['duration'],
                 "views": item['view_count'],
                 "thumbnail": item['thumbnail_url'],