chore: move pty and windows sandbox to Rust 2024 (#15954)

## Why

`codex-utils-pty` and `codex-windows-sandbox` were the remaining crates
in `codex-rs` that still overrode the workspace's Rust 2024 edition.
Moving them forward in a separate PR keeps the baseline edition update
isolated from the follow-on Bazel clippy workflow in #15955, while
making linting and formatting behavior consistent with the rest of the
workspace.

This PR also needs Cargo and Bazel to agree on the edition for
`codex-windows-sandbox`. Without the Bazel-side sync, the experimental
Bazel app-server builds fail once they compile `windows-sandbox-rs`.

## What changed

- switch `codex-rs/utils/pty` and `codex-rs/windows-sandbox-rs` to
`edition = "2024"`
- update `codex-utils-pty` callsites and tests to use the collapsed `if
let` form that Clippy expects under the new edition
- fix the Rust 2024 fallout in `windows-sandbox-rs`, including the
reserved `gen` identifier, `unsafe extern` requirements, and new Clippy
findings that surfaced under the edition bump
- keep the edition bump separate from a larger unsafe cleanup by
temporarily allowing `unsafe_op_in_unsafe_fn` in the Windows entrypoint
modules that now report it under Rust 2024
- update `codex-rs/windows-sandbox-rs/BUILD.bazel` to `crate_edition =
"2024"` so Bazel compiles the crate with the same edition as Cargo





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[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/15954).
* #15976
* #15955
* __->__ #15954

codex-rs/utils/pty/src/pipe.rs

@@ -3,9 +3,9 @@ use std::io;
 use std::io::ErrorKind;
 use std::path::Path;
 use std::process::Stdio;
-use std::sync::atomic::AtomicBool;
 use std::sync::Arc;
 use std::sync::Mutex as StdMutex;
+use std::sync::atomic::AtomicBool;
 
 use anyhow::Result;
 use tokio::io::AsyncRead;
@@ -64,11 +64,7 @@ fn kill_process(pid: u32) -> io::Result<()> {
         let success = winapi::um::processthreadsapi::TerminateProcess(handle, 1);
         let err = io::Error::last_os_error();
         winapi::um::handleapi::CloseHandle(handle);
-        if success == 0 {
-            Err(err)
-        } else {
-            Ok(())
-        }
+        if success == 0 { Err(err) } else { Ok(()) }
     }
 }