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/parser.h

@@ -14,6 +14,11 @@ typedef struct {
     size_t pos;
 } ASTNodeSlice;
 
+typedef struct {
+    Arena *arena;
+    AST tree;
+} ParseResult;
+
 ASTNode ASTNodeSlice_peek(ASTNodeSlice *slice);
 ASTNode ASTNodeSlice_next(ASTNodeSlice *slice);
 bool ASTNodeSlice_is_valid(ASTNodeSlice *slice);
@@ -24,7 +29,7 @@ ASTNode *led(ASTNodeSlice *slice, size_t right_precedence);
 uint8_t node_lbp(ASTNode node);
 uint8_t node_rbp(ASTNode node);
 
-AST parse(ASTNodeArray *arr);
-ASTNode *parse_expr(ASTNodeSlice *slice, uint8_t min_bp);
+ParseResult parse(ASTNodeArray *arr);
+ASTNode *parse_expr(ASTNodeSlice *slice, Arena *arena, uint8_t min_bp);
 
 #endif // !PARSER_H