Introduce some stricter typing

jedi/inference/base_value.py

@@ -9,6 +9,7 @@ just one.
 from functools import reduce
 from operator import add
 from itertools import zip_longest
+from typing import TYPE_CHECKING, Any
 
 from parso.python.tree import Name
 
@@ -21,12 +22,25 @@ from jedi.cache import memoize_method
 
 sentinel = object()
 
+if TYPE_CHECKING:
+    from jedi.inference import InferenceState
+
 
 class HasNoContext(Exception):
     pass
 
 
 class HelperValueMixin:
+    parent_context: Any
+    inference_state: "InferenceState"
+    name: Any
+    get_filters: Any
+    is_stub: Any
+    py__getattribute__alternatives: Any
+    py__iter__: Any
+    py__mro__: Any
+    _as_context: Any
+
     def get_root_context(self):
         value = self
         if value.parent_context is None:
@@ -499,7 +513,7 @@ class ValueSet:
         return ValueSet.from_sets(_getitem(c, *args, **kwargs) for c in self._set)
 
     def try_merge(self, function_name):
-        value_set = self.__class__([])
+        value_set = ValueSet([])
         for c in self._set:
             try:
                 method = getattr(c, function_name)