Simplify tuple flattening and destructuring

The `flatten_tuple` function was unnecessarily recursive. It can now
simply return the elements of the tuple directly. The VM's destructuring
logic has been updated to handle nested destructuring more efficiently.
A new integration test case for multi-level destructuring has been
added.

src/ast/compiler/specializer.rs

@@ -308,13 +308,7 @@ impl Specializer {
 
     fn flatten_tuple(&self, node: AnalyzedNode) -> Vec<AnalyzedNode> {
         match node.kind {
-            BoundKind::Tuple { elements } => {
-                let mut flat = Vec::new();
-                for el in elements {
-                    flat.extend(self.flatten_tuple(el));
-                }
-                flat
-            }
+            BoundKind::Tuple { elements } => elements,
             _ => vec![node],
         }
     }