Create stubs for toposort (#6048)

stubs/toposort/METADATA.toml

@@ -0,0 +1 @@
+version = "1.6"

stubs/toposort/toposort.pyi

@@ -0,0 +1,10 @@
+from typing import Any, Iterator, TypeVar
+
+_T = TypeVar("_T")
+
+class CircularDependencyError(ValueError):
+    data: dict[Any, set[Any]]
+    def __init__(self, data: dict[Any, set[Any]]) -> None: ...
+
+def toposort(data: dict[_T, set[_T]]) -> Iterator[set[_T]]: ...
+def toposort_flatten(data: dict[_T, set[_T]], sort: bool = ...) -> list[_T]: ...