fix: correct mutable reference handling and remove unused variables

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

src/compression_engine/program.rs

@@ -7,7 +7,6 @@ use std::io::{Read, Write};
 use std::os::unix::fs::PermissionsExt;
 use std::path::PathBuf;
 use std::process::{Child, Command, Stdio};
-use std::sync::Arc;
 
 use crate::compression_engine::CompressionEngine;