pass file into flex instead of content buffer

src/lexer/lexer.h

@@ -1,9 +1,10 @@
 #include "token.h"
 #include "../list/list.h"
+#include <stdio.h>
 
 typedef struct {
     const char *path;
-    const char *content;
+    FILE *file;
     int current_column;
     LinkedList* tokens;
     // add more fields as needed