Refactor: move os detection to own header

src/modules/os.c

@@ -1,5 +1,6 @@
 #include "fastfetch.h"
 #include "common/printing.h"
+#include "detection/os.h"
 
 #include <ctype.h>
 

src/modules/packages.c

@@ -4,6 +4,7 @@
 #include "common/printing.h"
 #include "common/settings.h"
 #include "common/processing.h"
+#include "detection/os.h"
 
 #include <stdlib.h>
 #include <string.h>