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/tui/src/app.rs

@@ -12,9 +12,9 @@ use crossterm::event::KeyCode;
 use crossterm::event::KeyEvent;
 use crossterm::event::MouseEvent;
 use crossterm::event::MouseEventKind;
-use std::sync::mpsc::channel;
 use std::sync::mpsc::Receiver;
 use std::sync::mpsc::Sender;
+use std::sync::mpsc::channel;
 
 /// Top‑level application state – which full‑screen view is currently active.
 enum AppState {