Add benchmark

upb_test/test.c

@@ -0,0 +1,13 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "hackers.upb.h"
+#include "hackers.upb_minitable.h"
+
+int main(void) {
+    upb_Arena *arena = upb_Arena_New();
+    Campaign *c = Campaign_new(arena);
+    (void)c;
+    printf("name: %.*s\n", (int)Campaign_name(c).size, Campaign_name(c).data);
+    upb_Arena_Free(arena);
+    return 0;
+}