[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/plugins/calculator.py

@@ -14,7 +14,7 @@ import babel
 import babel.numbers
 from flask_babel import gettext
 
-from searx.result_types import Answer
+from searx.result_types import EngineResults
 
 name = "Basic Calculator"
 description = gettext("Calculate mathematical expressions via the search bar")
@@ -94,8 +94,8 @@ def timeout_func(timeout, func, *args, **kwargs):
     return ret_val
 
 
-def post_search(request, search) -> list[Answer]:
-    results = []
+def post_search(request, search) -> EngineResults:
+    results = EngineResults()
 
     # only show the result of the expression on the first page
     if search.search_query.pageno > 1:
@@ -135,6 +135,6 @@ def post_search(request, search) -> list[Answer]:
         return results
 
     res = babel.numbers.format_decimal(res, locale=ui_locale)
-    Answer(results=results, answer=f"{search.search_query.query} = {res}")
+    results.add(results.types.Answer(answer=f"{search.search_query.query} = {res}"))
 
     return results