Macro impl_option_smart_i64_into_r 

macro_rules! impl_option_smart_i64_into_r {
    ($t:ty, $fits_i32:expr) => { ... };
}

Macro for NA-aware Option<T> → R smart scalar conversion. Checks if value fits i32 → INTSXP with NA_INTEGER for None, otherwise REALSXP with NA_REAL for None.