fix: add std::io imports and update finalize return type

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

src/meta_plugin/magic.rs

@@ -1,6 +1,7 @@
 use anyhow::Result;
 use magic::{Cookie, CookieFlags};
 use rusqlite::Connection;
+use std::io;
 
 use crate::meta_plugin::MetaPlugin;