pub(super) fn new_inner<M, const BIASED: bool>(
message_stream: BoxStream<'static, StreamExecutorResult<Either<Message, M>>>,
data_stream: BoxStream<'static, StreamExecutorResult<Either<Message, M>>>,
) -> SelectWithStrategy<BoxStream<'static, StreamExecutorResult<Either<Message, M>>>, BoxStream<'static, StreamExecutorResult<Either<Message, M>>>, impl FnMut(&mut PollNext) -> PollNext, PollNext>