Function nova_rt_task_sleep_future_nanos 

#[unsafe(no_mangle)]
pub extern "C-unwind" fn nova_rt_task_sleep_future_nanos(
    nanos: i64,
) -> *mut u8

A fresh Future<unit> that parks for nanos nanoseconds, then completes.

Same layout obligation as nova_rt_task_yield_future: a scanned FUTURE_SIZE fat pointer over a scanned state object, built to the layout async_lower.rs independently emits. A fresh state object per call, because the deadline is per-suspension.