[Pillow] Annotate ImageSequence.pyi (#11625)

stubs/Pillow/PIL/ImageSequence.pyi

@@ -1,11 +1,14 @@
-from _typeshed import Incomplete
+from collections.abc import Callable
+from typing_extensions import Self
+
+from .Image import Image
 
 class Iterator:
-    im: Incomplete
-    position: Incomplete
-    def __init__(self, im) -> None: ...
-    def __getitem__(self, ix): ...
-    def __iter__(self): ...
-    def __next__(self): ...
+    im: Image
+    position: int
+    def __init__(self, im: Image) -> None: ...
+    def __getitem__(self, ix: int) -> Image: ...
+    def __iter__(self) -> Self: ...
+    def __next__(self) -> Image: ...
 
-def all_frames(im, func: Incomplete | None = None): ...
+def all_frames(im: Image | list[Image], func: Callable[[Image], Image] | None = None) -> list[Image]: ...