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/vm.rs

@@ -416,7 +416,15 @@ impl VM {
                                 {
                                     self.stack.extend(arg_vals);
                                 } else {
-                                    self.unpack(&closure.parameter_node, &arg_vals, &mut 0)?;
+                                    // Map each parameter pattern to the provided arguments
+                                    if let BoundKind::Tuple { elements } = &closure.parameter_node.kind {
+                                        let mut offset = 0;
+                                        for el in elements {
+                                            self.unpack(el, &arg_vals, &mut offset)?;
+                                        }
+                                    } else {
+                                        self.unpack(&closure.parameter_node, &arg_vals, &mut 0)?;
+                                    }
                                 }
                                 let result = self.eval_internal(obs, &closure.exec_node);
                                 self.frames.pop();