python: typing stubs: import typing for Sequence return types

SequenceTypeNode and ClassTypeNode always format as _typing.Sequence[...]
and _typing.Type[...], but ContainerTypeNode only reports the typing
import as required when compatible_to_runtime_usage is set. Stubs for
modules that use these nodes without any other _typing usage (e.g.
cv2/videoio_registry) reference _typing without importing it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

modules/python/src2/typing_stubs_generation/nodes/type_node.py

@@ -740,6 +740,11 @@ class SequenceTypeNode(ContainerTypeNode):
     def type_format(self) -> str:
         return "_typing.Sequence[{}]"
 
+    @property
+    def required_usage_imports(self) -> Generator[str, None, None]:
+        yield "import typing as _typing"
+        yield from super().required_usage_imports
+
     @property
     def types_separator(self) -> str:
         return ", "
@@ -896,6 +901,11 @@ class ClassTypeNode(ContainerTypeNode):
     def type_format(self) -> str:
         return "_typing.Type[{}]"
 
+    @property
+    def required_usage_imports(self) -> Generator[str, None, None]:
+        yield "import typing as _typing"
+        yield from super().required_usage_imports
+
     @property
     def types_separator(self) -> str:
         return ", "