[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/chefkoch.py

@@ -43,7 +43,7 @@ def response(resp):
 
         publishedDate = None
         if recipe['submissionDate']:
-            publishedDate = datetime.strptime(result['recipe']['submissionDate'][:19], "%Y-%m-%dT%H:%M:%S")
+            publishedDate = datetime.fromisoformat(result['recipe']['submissionDate'][:19])
 
         content = [
             f"Schwierigkeitsstufe (1-3): {recipe['difficulty']}",