[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/arxiv.py

@@ -109,7 +109,7 @@ def response(resp: "SXNG_Response") -> EngineResults:
         comments_elements = eval_xpath_getindex(entry, xpath_comment, 0, default=None)
         comments: str = "" if comments_elements is None else comments_elements.text
 
-        publishedDate = datetime.strptime(eval_xpath_getindex(entry, xpath_published, 0).text, "%Y-%m-%dT%H:%M:%SZ")
+        publishedDate = datetime.fromisoformat(eval_xpath_getindex(entry, xpath_published, 0).text.rstrip("Z"))
 
         res.add(
             res.types.Paper(