[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/tagesschau.py

@@ -81,7 +81,7 @@ def _story(item):
     return {
         'title': item['title'],
         'thumbnail': item.get('teaserImage', {}).get('imageVariants', {}).get('16x9-256'),
-        'publishedDate': datetime.strptime(item['date'][:19], '%Y-%m-%dT%H:%M:%S'),
+        'publishedDate': datetime.fromisoformat(item['date'][:19]),
         'content': item.get('firstSentence'),
         'url': item['shareURL'] if use_source_url else item['detailsweb'],
     }
@@ -103,7 +103,7 @@ def _video(item):
         'template': 'videos.html',
         'title': title,
         'thumbnail': item.get('teaserImage', {}).get('imageVariants', {}).get('16x9-256'),
-        'publishedDate': datetime.strptime(item['date'][:19], '%Y-%m-%dT%H:%M:%S'),
+        'publishedDate': datetime.fromisoformat(item['date'][:19]),
         'content': item.get('firstSentence', ''),
         'iframe_src': video_url,
         'url': url,