fix: restrict self to sized types and clone response in process_chunk and finalize_plugins

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/meta_plugin.rs

@@ -260,7 +260,7 @@ pub trait MetaPlugin {
     }
     
     // Method to downcast to concrete type (for checking finalization state)
-    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any where Self: Sized {
         self
     }
 }