rework: AST now uses an arena for allocation

For now it works but i dont really like that i use ParseResult, i mean
is necessary but i think i will try to make it cleaner so that i can
just directly use like parse and pass tath into evaluate, that would
require to move the main evaluate funciton into evaluate_tree or
something  and evaluate takes the arena, uses evaluate_tree and frees
the arena, will try that the next commit but for now this version works
perfectly.

include/evaluator.h

@@ -2,7 +2,6 @@
 #define EVALUATOR_H
 
 #include "lexer.h"
-#include "arena.h"
 #include <stdint.h>
 
 int64_t evaluate(ASTNode *tree);