[refactor] typification of SearXNG / EngineResults

In [1] and [2] we discussed the need of a Result.results property and how we can
avoid unclear code.  This patch implements a class for the reslut-lists of
engines::

    searx.result_types.EngineResults

A simple example for the usage in engine development::

    from searx.result_types import EngineResults
    ...
    def response(resp) -> EngineResults:
        res = EngineResults()
        ...
        res.add( res.types.Answer(answer="lorem ipsum ..", url="https://example.org") )
        ...
        return res

[1] https://github.com/searxng/searxng/pull/4183#pullrequestreview-257400034
[2] https://github.com/searxng/searxng/pull/4183#issuecomment-2614301580
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/engines/duckduckgo.py

@@ -27,7 +27,7 @@ from searx.network import get  # see https://github.com/searxng/searxng/issues/7
 from searx import redisdb
 from searx.enginelib.traits import EngineTraits
 from searx.exceptions import SearxEngineCaptchaException
-from searx.result_types import Answer
+from searx.result_types import EngineResults
 
 if TYPE_CHECKING:
     import logging
@@ -355,12 +355,12 @@ def is_ddg_captcha(dom):
     return bool(eval_xpath(dom, "//form[@id='challenge-form']"))
 
 
-def response(resp):
+def response(resp) -> EngineResults:
+    results = EngineResults()
 
     if resp.status_code == 303:
-        return []
+        return results
 
-    results = []
     doc = lxml.html.fromstring(resp.text)
 
     if is_ddg_captcha(doc):
@@ -398,8 +398,15 @@ def response(resp):
         and "URL Decoded:" not in zero_click
     ):
         current_query = resp.search_params["data"].get("q")
-
-        Answer(results=results, answer=zero_click, url="https://duckduckgo.com/?" + urlencode({"q": current_query}))
+        results.add(
+            results.types.Answer(
+                answer=zero_click,
+                url="https://duckduckgo.com/?"
+                + urlencode(
+                    {"q": current_query},
+                ),
+            )
+        )
 
     return results