Optimize header values (#201)

* Optimize serialization threshold

* Size unserialization chunk size to 64mb

Author: shikokuchuo

src/nanonext.h

@@ -120,8 +120,8 @@ extern int R_interrupts_pending;
 #define ERROR_RET(xc) { Rf_warning("%d | %s", xc, nng_strerror(xc)); return mk_error(xc); }
 #define NANONEXT_INIT_BUFSIZE 4096
 #define NANONEXT_SERIAL_VER 3
-#define NANONEXT_SERIAL_THR 134217728
-#define NANONEXT_CHUNK_SIZE INT_MAX // must be <= INT_MAX
+#define NANONEXT_SERIAL_THR 67108864
+#define NANONEXT_CHUNK_SIZE 67108864 // must be <= INT_MAX
 #define NANONEXT_STR_SIZE 40
 #define NANONEXT_WAIT_DUR 1000
 #define NANO_ALLOC(x, sz)                                      \