[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/quark.py

@@ -292,7 +292,7 @@ def parse_news_uchq(data):
     results = []
     for item in data.get('feed', []):
         try:
-            published_date = datetime.strptime(item.get('time'), "%Y-%m-%d")
+            published_date = datetime.fromisoformat(item.get('time'))
         except (ValueError, TypeError):
             # Sometime Quark will return non-standard format like "1天前", set published_date as None
             published_date = None