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





---
[//]: # (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/windows-sandbox-rs/src/helper_materialization.rs

@@ -45,12 +45,12 @@ pub(crate) fn helper_bin_dir(codex_home: &Path) -> PathBuf {
 }
 
 pub(crate) fn legacy_lookup(kind: HelperExecutable) -> PathBuf {
-    if let Ok(exe) = std::env::current_exe() {
-        if let Some(dir) = exe.parent() {
-            let candidate = dir.join(kind.file_name());
-            if candidate.exists() {
-                return candidate;
-            }
+    if let Ok(exe) = std::env::current_exe()
+        && let Some(dir) = exe.parent()
+    {
+        let candidate = dir.join(kind.file_name());
+        if candidate.exists() {
+            return candidate;
         }
     }
     PathBuf::from(kind.file_name())
@@ -377,4 +377,3 @@ mod tests {
         );
     }
 }
-