Refactor environment to use stack-based scoping

The commit rewrites the environment to use a stack of hash maps for
managing variable scopes. This replaces the old parent-reference
approach with a simpler and more efficient stack-based model.

Key changes: - Rename Environment to EnvironmentStack - Store scopes in
a Vec of HashMaps - Add push/pop scope operations for block handling -
Update interpreter to properly manage scope lifetimes - Clean up error
handling with helper functions

example.lox

@@ -13,10 +13,11 @@ do
     cavallo
 end
 do
+    var cavallo = 0;
     print "cavallo";
     while cavallo < 10 do
-        print "loop: " + cavallo;
         cavallo = cavallo + 1;
+        print cavallo;
     end
     89
 end