[mojo-stdlib] Minor cleanups for Tuple, NFC.

These are just minor improvements to `Tuple` from a walkthrough
with @VerdagonModular.

MODULAR_ORIG_COMMIT_REV_ID: 352c9d3bc6494f4696a405bf3d992cfced5dce89

stdlib/src/builtin/tuple.mojo

@@ -81,8 +81,10 @@ struct Tuple[*element_types: CollectionElement](Sized, CollectionElement):
                 UnsafePointer.address_of(self[i])
             )
 
-        # Mark the elements as destroyed.
-        storage._is_owned = False
+        # Do not destroy the elements when 'storage' goes away.
+        __mlir_op.`lit.ownership.mark_destroyed`(
+            __get_mvalue_as_litref(storage)
+        )
 
     fn __del__(owned self):
         """Destructor that destroys all of the elements."""
@@ -126,6 +128,7 @@ struct Tuple[*element_types: CollectionElement](Sized, CollectionElement):
             UnsafePointer.address_of(existing[i]).move_pointee_into(
                 UnsafePointer.address_of(self[i])
             )
+        # Note: The destructor on `existing` is auto-disabled in a moveinit.
 
     @always_inline
     @staticmethod