Annotate known magic-method return types (#9131)

stubs/cffi/_cffi_backend.pyi

@@ -61,44 +61,44 @@ class Lib:
 class _CDataBase:
     __name__: ClassVar[str]
     def __add__(self, other): ...
-    def __bool__(self): ...
+    def __bool__(self) -> bool: ...
     def __call__(self, *args, **kwargs): ...
-    def __complex__(self): ...
-    def __delitem__(self, other): ...
+    def __complex__(self) -> complex: ...
+    def __delitem__(self, other) -> None: ...
     def __dir__(self): ...
     def __enter__(self): ...
     def __eq__(self, other): ...
     def __exit__(self, type, value, traceback): ...
-    def __float__(self): ...
+    def __float__(self) -> float: ...
     def __ge__(self, other): ...
     def __getitem__(self, index): ...
     def __gt__(self, other): ...
-    def __hash__(self): ...
-    def __int__(self): ...
+    def __hash__(self) -> int: ...
+    def __int__(self) -> int: ...
     def __iter__(self): ...
     def __le__(self, other): ...
-    def __len__(self): ...
+    def __len__(self) -> int: ...
     def __lt__(self, other): ...
     def __ne__(self, other): ...
     def __radd__(self, other): ...
     def __rsub__(self, other): ...
-    def __setitem__(self, index, object): ...
+    def __setitem__(self, index, object) -> None: ...
     def __sub__(self, other): ...
 
 @final
 class buffer:
     __hash__: ClassVar[None]  # type: ignore[assignment]
     def __init__(self, *args, **kwargs) -> None: ...
-    def __delitem__(self, other): ...
+    def __delitem__(self, other) -> None: ...
     def __eq__(self, other): ...
     def __ge__(self, other): ...
     def __getitem__(self, index): ...
     def __gt__(self, other): ...
     def __le__(self, other): ...
-    def __len__(self): ...
+    def __len__(self) -> int: ...
     def __lt__(self, other): ...
     def __ne__(self, other): ...
-    def __setitem__(self, index, object): ...
+    def __setitem__(self, index, object) -> None: ...
 
 # These aliases are to work around pyright complaints.
 # Pyright doesn't like it when a class object is defined as an alias

stubs/cffi/cffi/backend_ctypes.pyi

@@ -18,11 +18,11 @@ class CTypesData:
     def __le__(self, other): ...
     def __gt__(self, other): ...
     def __ge__(self, other): ...
-    def __hash__(self): ...
+    def __hash__(self) -> int: ...
     def __repr__(self, c_name: str | None = ...): ...
 
 class CTypesGenericPrimitive(CTypesData):
-    def __hash__(self): ...
+    def __hash__(self) -> int: ...
 
 class CTypesGenericArray(CTypesData):
     def __iter__(self): ...

stubs/cffi/cffi/model.pyi

@@ -21,7 +21,7 @@ class BaseTypeByIdentity:
 class BaseType(BaseTypeByIdentity):
     def __eq__(self, other): ...
     def __ne__(self, other): ...
-    def __hash__(self): ...
+    def __hash__(self) -> int: ...
 
 class VoidType(BaseType):
     c_name_with_marker: str