[refactor] typification of SearXNG (MainResult) / result items (part 2)

The class ReslutContainer has been revised, it can now handle the typed Result
items of classes:

- MainResult
- LegacyResult (a dict wrapper for backward compatibility)

Due to the now complete typing of theses three clases, instead of the *getitem*
accesses, the fields can now be accessed directly via attributes (which is also
supported by the IDE).

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/enginelib/__init__.py

@@ -142,3 +142,6 @@ class Engine:  # pylint: disable=too-few-public-methods
     tokens: List[str]
     """A list of secret tokens to make this engine *private*, more details see
     :ref:`private engines`."""
+
+    weight: int
+    """Weighting of the results of this engine (:ref:`weight <settings engines>`)."""