feat: Add pipe parameter validation and fix VM call frame

Adds a check within the `PipeHook` to ensure the number of input streams
provided to a `pipe` operation matches the number of parameters expected
by the associated lambda function. This prevents runtime errors and
provides a clearer compile-time diagnostic.

Additionally, this commit corrects the order in which a `CallFrame` is
pushed onto the VM's frame stack. By pushing the frame earlier, it
ensures that slow-path `unpack` operations have access to a valid frame,
preventing "No call frame" errors.

src/ast/vm.rs

@@ -239,6 +239,13 @@ impl VM {
         self.stack.clear();
         self.frames.clear();
 
+        // Push the call frame early so that `unpack` (slow path) can use
+        // `set_value` / `get_value`, which require a valid call frame.
+        self.frames.push(CallFrame {
+            stack_base: 0,
+            closure: Some(closure_rc.clone()),
+        });
+
         let closure = closure_rc.as_ref();
         if let Some(count) = closure.positional_count
             && args.len() == count as usize
@@ -254,11 +261,6 @@ impl VM {
             self.stack.resize(closure.stack_size as usize, Value::Void);
         }
 
-        self.frames.push(CallFrame {
-            stack_base: 0,
-            closure: Some(closure_rc.clone()),
-        });
-
         let result = self.eval_internal(observer, &closure.exec_node);
         self.frames.pop();
         self.resolve_tail_calls(observer, result)