refactor: move allow_binary logic to async_item_service

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

src/services/async_item_service.rs

@@ -1,11 +1,14 @@
 use crate::services::error::CoreError;
 use crate::services::item_service::ItemService;
 use crate::services::types::{ItemWithContent, ItemWithMeta};
+use crate::common::is_binary::is_binary;
 use rusqlite::Connection;
 use std::collections::HashMap;
 use std::path::PathBuf;
 use std::sync::Arc;
 use tokio::sync::Mutex;
+use tokio::io::{AsyncReadExt, AsyncSeekExt};
+use tokio_util::io::ReaderStream;
 
 /// An asynchronous wrapper around the `ItemService` for use in async contexts like the web server.
 /// It uses `tokio::task::spawn_blocking` to run synchronous database and filesystem operations