fix: implement debug for meta plugin program and remove unused imports

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

src/meta_plugin/magic.rs

@@ -132,7 +132,7 @@ impl MetaPlugin for MagicFileMetaPlugin {
             
             // Check if we've reached our buffer limit and save if so
             if self.buffer.len() >= self.max_buffer_size && !self.is_saved {
-                if let (Some(conn), Some(item_id)) = (self.conn, self.item_id) {
+                if let (Some(_conn), Some(_item_id)) = (self.conn, self.item_id) {
                     if let Err(e) = self.save_all_magic_metadata() {
                         eprintln!("Warning: Failed to save magic metadata early: {}", e);
                     }