Update cargo to 2024 edition (#842)

Some effects of this change:
- New formatting changes across many files. No functionality changes
should occur from that.
- Calls to `set_env` are considered unsafe, since this only happens in
tests we wrap them in `unsafe` blocks

codex-rs/core/src/mcp_connection_manager.rs

@@ -8,9 +8,9 @@
 
 use std::collections::HashMap;
 
-use anyhow::anyhow;
 use anyhow::Context;
 use anyhow::Result;
+use anyhow::anyhow;
 use codex_mcp_client::McpClient;
 use mcp_types::Tool;
 use tokio::task::JoinSet;