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/execpolicy/tests/parse_sed_command.rs

@@ -1,5 +1,5 @@
-use codex_execpolicy::parse_sed_command;
 use codex_execpolicy::Error;
+use codex_execpolicy::parse_sed_command;
 
 #[test]
 fn parses_simple_print_command() {