[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/findthatmeme.py

@@ -37,7 +37,7 @@ def response(resp):
     for item in search_res:
         img = 'https://s3.thehackerblog.com/findthatmeme/' + item['image_path']
         thumb = 'https://s3.thehackerblog.com/findthatmeme/thumb/' + item.get('thumbnail', '')
-        date = datetime.strptime(item["updated_at"].split("T")[0], "%Y-%m-%d")
+        date = datetime.fromisoformat(item["updated_at"].split("T")[0])
         formatted_date = datetime.fromtimestamp(date.timestamp())
 
         results.append(