fix: print timestamp in a portable way

examples/unix/c11/z_sub_attachment.c

@@ -13,6 +13,7 @@
 //
 
 #include <ctype.h>
+#include <inttypes.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -83,7 +84,7 @@ void data_handler(const z_loaned_sample_t *sample, void *ctx) {
     // Check timestamp
     const z_timestamp_t *ts = z_sample_timestamp(sample);
     if (ts != NULL) {
-        printf("    with timestamp: %ld\n", z_timestamp_npt64_time(ts));
+        printf("    with timestamp: %" PRIu64 "\n", z_timestamp_npt64_time(ts));
     }
     // Check attachment
     kv_pairs_t kvp = {.current_idx = 0, .len = KVP_LEN, .data = (kv_pair_t *)malloc(KVP_LEN * sizeof(kv_pair_t))};