fix: update trait and remove unused io imports

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

src/meta_plugin/digest.rs

@@ -1,6 +1,5 @@
 use anyhow::Result;
 use sha2::{Digest, Sha256};
-use std::io;
 use std::time::Instant;
 
 use crate::meta_plugin::MetaPlugin;