Function sled_iter_next 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn sled_iter_next(
    iter: *mut Iter,
    key: *mut *const c_char,
    keylen: *mut size_t,
    val: *mut *const c_char,
    vallen: *mut size_t,
) -> c_uchar

Get they next kv pair from an iterator. Caller is responsible for freeing the key and value with sled_free_buf. Returns 0 when exhausted.