Refactored the scanner and updated the Token struct to store the length of its lexeme to avoid malloc()ing new strings for every token.

scanner.h

@@ -31,8 +31,9 @@ typedef enum {
 
 typedef struct {
     TokenType type;
-    char* lexeme;
+    const char* lexeme;
     int line;
+    int length;
 } Token;
 
 typedef struct {