fix/refactor: Modified evaluate and changed it to evaluate_tree

So i did what the last commit said, also fixed parse_expr because it was
still using malloc for allocating new nodes so i made it use arena_alloc
like it should, did the very first tests so it's all good, i think is
readdy to merge.

include/evaluator.h

@@ -2,8 +2,10 @@
 #define EVALUATOR_H
 
 #include "lexer.h"
+#include "parser.h"
 #include <stdint.h>
 
-int64_t evaluate(ASTNode *tree);
+int64_t evaluate(ParseResult context);
+int64_t evaluate_tree(ASTNode *tree);
 
 #endif // !EVALUATOR_H