stdlib: add __slots__ (#14611)

stdlib/pickletools.pyi

@@ -15,6 +15,7 @@ TAKEN_FROM_ARGUMENT4U: Final = -4
 TAKEN_FROM_ARGUMENT8U: Final = -5
 
 class ArgumentDescriptor:
+    __slots__ = ("name", "n", "reader", "doc")
     name: str
     n: int
     reader: _Reader
@@ -118,6 +119,7 @@ def read_long4(f: IO[bytes]) -> int: ...
 long4: ArgumentDescriptor
 
 class StackObject:
+    __slots__ = ("name", "obtype", "doc")
     name: str
     obtype: type[Any] | tuple[type[Any], ...]
     doc: str
@@ -143,6 +145,7 @@ markobject: StackObject
 stackslice: StackObject
 
 class OpcodeInfo:
+    __slots__ = ("name", "code", "arg", "stack_before", "stack_after", "proto", "doc")
     name: str
     code: str
     arg: ArgumentDescriptor | None