fix: add missing clone_box impls for gzip and lz4 engines

Co-authored-by: aider (openai/andrew/openrouter/sonoma-sky-alpha) <aider@aider.chat>

src/compression_engine/lz4.rs

@@ -34,4 +34,8 @@ impl CompressionEngine for CompressionEngineLZ4 {
 
         Ok(Box::new(lz4_write))
     }
+
+    fn clone_box(&self) -> Box<dyn CompressionEngine> {
+        Box::new(self.clone())
+    }
 }