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/common/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "codex-common"
 version = "0.1.0"
-edition = "2021"
+edition = "2024"
 
 [dependencies]
 chrono = { version = "0.4.40", optional = true }