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/src/error.rs

@@ -4,8 +4,8 @@ use serde::Serialize;
 
 use crate::arg_matcher::ArgMatcher;
 use crate::arg_resolver::PositionalArg;
-use serde_with::serde_as;
 use serde_with::DisplayFromStr;
+use serde_with::serde_as;
 
 pub type Result<T> = std::result::Result<T, Error>;