Annotate type on abstract/_function_base.py, and also correct some ty…

…pes on _base.py and _classes.py that were incorrect.

Also remove the actual return statement from `SignedFunction._check_paramspec_args` as there was only a single place being called, and the return was not being used.

PiperOrigin-RevId: 688604582

pytype/abstract/_base.py

@@ -183,7 +183,10 @@ def property_get(
     return self
 
   def get_special_attribute(
-      self, unused_node: "cfg.CFGNode", name: str, unused_valself: "cfg.Binding"
+      self,
+      unused_node: "cfg.CFGNode",
+      name: str,
+      unused_valself: "cfg.Variable",
   ) -> "cfg.Variable | None":
     """Fetch a special attribute (e.g., __get__, __iter__)."""
     if name == "__class__":

pytype/abstract/_classes.py

@@ -1265,7 +1265,7 @@ def getitem_slot(
     )
 
   def get_special_attribute(
-      self, node: cfg.CFGNode, name: str, valself: cfg.Binding
+      self, node: cfg.CFGNode, name: str, valself: cfg.Variable
   ) -> cfg.Variable | None:
     if (
         valself