[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/result_types/__init__.py

@@ -9,10 +9,50 @@
    gradually.  For more, please read :ref:`result types`.
 
 """
+# pylint: disable=too-few-public-methods
 
 from __future__ import annotations
 
-__all__ = ["Result", "AnswerSet", "Answer", "Translations"]
+__all__ = ["Result", "EngineResults", "AnswerSet", "Answer", "Translations"]
+
+import abc
+
+from searx import enginelib
 
 from ._base import Result, LegacyResult
 from .answer import AnswerSet, Answer, Translations
+
+
+class ResultList(list, abc.ABC):
+    """Base class of all result lists (abstract)."""
+
+    class types:  # pylint: disable=invalid-name
+        """The collection of result types (which have already been implemented)."""
+
+        Answer = Answer
+        Translations = Translations
+
+    def __init__(self):
+        # pylint: disable=useless-parent-delegation
+        super().__init__()
+
+    def add(self, result: Result):
+        """Add a :py:`Result` item to the result list."""
+        self.append(result)
+
+
+class EngineResults(ResultList):
+    """Result list that should be used by engine developers.  For convenience,
+    engine developers don't need to import types / see :py:obj:`ResultList.types`.
+
+    .. code:: python
+
+       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
+    """

searx/result_types/_base.py

@@ -53,27 +53,6 @@ class Result(msgspec.Struct, kw_only=True):
     The field is optional and is initialized from the context if necessary.
     """
 
-    results: list = []  # https://jcristharif.com/msgspec/structs.html#default-values
-    """Result list of an :origin:`engine <searx/engines>` response or a
-    :origin:`answerer <searx/answerers>` to which the answer should be added.
-
-    This field is only present for the sake of simplicity.  Typically, the
-    response function of an engine has a result list that is returned at the
-    end. By specifying the result list in the constructor of the result, this
-    result is then immediately added to the list (this parameter does not have
-    another function).
-
-    .. code:: python
-
-       def response(resp):
-           results = []
-           ...
-           Answer(results=results, answer=answer, url=url)
-           ...
-           return results
-
-    """
-
     def normalize_result_fields(self):
         """Normalize a result ..
 
@@ -92,9 +71,7 @@ class Result(msgspec.Struct, kw_only=True):
                 self.url = self.parsed_url.geturl()
 
     def __post_init__(self):
-        """Add *this* result to the result list."""
-
-        self.results.append(self)
+        pass
 
     def __hash__(self) -> int:
         """Generates a hash value that uniquely identifies the content of *this*