Add @disjoint_base decorator in the stdlib (#14599)

And fix some other new stubtest finds.

stdlib/_struct.pyi

@@ -1,6 +1,7 @@
 from _typeshed import ReadableBuffer, WriteableBuffer
 from collections.abc import Iterator
 from typing import Any
+from typing_extensions import disjoint_base
 
 def pack(fmt: str | bytes, /, *v: Any) -> bytes: ...
 def pack_into(fmt: str | bytes, buffer: WriteableBuffer, offset: int, /, *v: Any) -> None: ...
@@ -8,7 +9,7 @@ def unpack(format: str | bytes, buffer: ReadableBuffer, /) -> tuple[Any, ...]: .
 def unpack_from(format: str | bytes, /, buffer: ReadableBuffer, offset: int = 0) -> tuple[Any, ...]: ...
 def iter_unpack(format: str | bytes, buffer: ReadableBuffer, /) -> Iterator[tuple[Any, ...]]: ...
 def calcsize(format: str | bytes, /) -> int: ...
-
+@disjoint_base
 class Struct:
     @property
     def format(self) -> str: ...