Use GB macro to define arena size

src/main.c

@@ -1,6 +1,7 @@
 #include "img.h"
 #include "mem_arena.h"
 #include "mem_utils.h"
+#include "misc_utils.h"
 #include "obj.h"
 #include "render.h"
 #include "shaders.h"
@@ -21,8 +22,7 @@ enum {
 
 int main(void) {
   Arena *arena = NULL;
-  if (!wapp_mem_arena_init(&arena, 10ul * 1024ul * 1024ul * 1024ul,
-                           WAPP_MEM_ALLOC_RESERVE, false)) {
+  if (!wapp_mem_arena_init(&arena, GB(10), WAPP_MEM_ALLOC_RESERVE, false)) {
     return TINY_EXIT_ARENA_INIT_FAILED;
   }
 

src/utils/utils.h

@@ -2,6 +2,7 @@
 #define UTILS_H
 
 #include "aliases.h"
+
 #define swap(T, v0, v1)                                                        \
   do {                                                                         \
     T tmp = v0;                                                                \