Macro impl_vec_option_smart_i64_into_r 

macro_rules! impl_vec_option_smart_i64_into_r {
    ($t:ty, $fits_i32:expr) => { ... };
}

Macro for NA-aware Vec<Option<T>> → R smart vector conversion. Checks if all non-None values fit i32 → INTSXP, otherwise REALSXP.

Allocates the R vector directly and coerces in-place — no intermediate Vec.