Some aggressive changes to silence a significant number of type errors.

Error count: 90 -> 66

manim/scene/scene.py

@@ -119,7 +119,7 @@ def __init__(
         # TODO: We should probably change the default value to the empty list.
         # This would remove several type issues, but it also triggers a lot of
         # errors in the unittests (pytest)
-        self.animations: list[Animation] | None = None
+        self.animations: list[Animation] = []
         self.stop_condition: Callable[[], bool] | None = None
         self.moving_mobjects: list[Mobject] = []
         self.static_mobjects: list[Mobject] = []
@@ -128,7 +128,7 @@ def __init__(
         # TODO: We should probably change the default value to 0, to avoid
         # handling the case where the value is None.
         # This change triggers no errors in the unittests (pytest).
-        self.last_t: float | None = None
+        self.last_t: float = 0
         self.queue: Queue = Queue()
         self.skip_animation_preview = False
         self.meshes: list[Object3D] = []

manim/scene/scene_file_writer.py

@@ -553,7 +553,7 @@ def open_partial_movie_stream(self, file_path: str | None = None) -> None:
             partial_movie_file_pix_fmt = "argb"
 
         with av.open(file_path, mode="w") as video_container:
-            stream = video_container.add_stream(
+            stream: Any = video_container.add_stream(
                 partial_movie_file_codec,
                 rate=fps,
                 options=av_options,
@@ -643,7 +643,7 @@ def combine_files(
         output_container.metadata["comment"] = (
             f"Rendered with Manim Community v{__version__}"
         )
-        output_stream = output_container.add_stream(
+        output_stream: Any = output_container.add_stream(
             codec_name="gif" if create_gif else None,
             template=partial_movies_stream if not create_gif else None,
         )