Refactor headers and remove platform-specific directives

Removed the `#define _GNU_SOURCE` directive and the `#ifdef _WIN32` block along with its corresponding `#else` block. Added `#include "mex.h"`, `#include "../AppModel/include/app_api.h"`, and `#include <string.h>`. These changes streamline the code by removing platform-specific dependencies and incorporating the MEX API and application model headers.

OctaveMex/octavelibczi.c

@@ -1,4 +1,3 @@
-#define MX_HAS_INTERLEAVED_COMPLEX 1
 #define _GNU_SOURCE
 #ifdef _WIN32
 #include <Windows.h>
@@ -9,6 +8,7 @@
 #include <unistd.h>
 #endif
 
+#define MX_HAS_INTERLEAVED_COMPLEX 1
 #include "mex.h"
 #include "../AppModel/include/app_api.h"
 #include <string.h>