Fix some typehints in mobject.py (#3668)

* refactor(mobject): fix some typehints

* Move typing_extensions import under `if TYPE_CHECKING`
* Change from using `def animate(self: T ,...) -> T` to `def
  animate(self, ...) -> Self` as stated in PEP 673
* Fix incorrect usage of `T` in a method

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* move updaters type alias into TYPE_CHECKING

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: JasonGrace2282

manim/animation/speedmodifier.py

@@ -4,15 +4,18 @@
 
 import inspect
 import types
-from typing import Callable
+from typing import TYPE_CHECKING, Callable
 
 from numpy import piecewise
 
 from ..animation.animation import Animation, Wait, prepare_animation
 from ..animation.composition import AnimationGroup
-from ..mobject.mobject import Mobject, Updater, _AnimationBuilder
+from ..mobject.mobject import Mobject, _AnimationBuilder
 from ..scene.scene import Scene
 
+if TYPE_CHECKING:
+    from ..mobject.mobject import Updater
+
 __all__ = ["ChangeSpeed"]
 
 

manim/mobject/mobject.py

@@ -16,10 +16,9 @@
 import warnings
 from functools import partialmethod, reduce
 from pathlib import Path
-from typing import TYPE_CHECKING, Callable, Iterable, Literal, TypeVar, Union
+from typing import TYPE_CHECKING, Callable, Iterable, Literal
 
 import numpy as np
-from typing_extensions import Self, TypeAlias
 
 from manim.mobject.opengl.opengl_compatibility import ConvertToOpenGL
 
@@ -39,14 +38,9 @@
 from ..utils.paths import straight_path
 from ..utils.space_ops import angle_between_vectors, normalize, rotation_matrix
 
-# TODO: Explain array_attrs
-
-TimeBasedUpdater: TypeAlias = Callable[["Mobject", float], None]
-NonTimeBasedUpdater: TypeAlias = Callable[["Mobject"], None]
-Updater: TypeAlias = Union[NonTimeBasedUpdater, TimeBasedUpdater]
-T = TypeVar("T", bound="Mobject")
-
 if TYPE_CHECKING:
+    from typing_extensions import Self, TypeAlias
+
     from manim.typing import (
         FunctionOverride,
         Image,
@@ -61,6 +55,10 @@
 
     from ..animation.animation import Animation
 
+    TimeBasedUpdater: TypeAlias = Callable[["Mobject", float], object]
+    NonTimeBasedUpdater: TypeAlias = Callable[["Mobject"], object]
+    Updater: TypeAlias = NonTimeBasedUpdater | TimeBasedUpdater
+
 
 class Mobject:
     """Mathematical Object: base class for objects that can be displayed on screen.
@@ -237,7 +235,7 @@ def construct(self):
             cls.__init__ = cls._original__init__
 
     @property
-    def animate(self: T) -> _AnimationBuilder | T:
+    def animate(self) -> _AnimationBuilder | Self:
         """Used to animate the application of any method of :code:`self`.
 
         Any method called on :code:`animate` is converted to an animation of applying
@@ -2926,7 +2924,7 @@ def set_z_index(
         self,
         z_index_value: float,
         family: bool = True,
-    ) -> T:
+    ) -> Self:
         """Sets the :class:`~.Mobject`'s :attr:`z_index` to the value specified in `z_index_value`.
 
         Parameters