Add macOS Seatbelt filesystem integration tests (#39665)

## What changed

Add macOS-only integration coverage that runs commands under the production
Seatbelt policy and verifies:

- deny globs protect matching files, directory ancestors, symlink aliases, and
  paths created after policy application;
- protected directories cannot be moved, replaced, or exchanged across
  writable roots; and
- standard read-only and workspace-write profiles continue to allow expected
  filesystem operations.

GitOrigin-RevId: 1f666835ee402bedd1d32e87f1082eaaf7b7bf6a

codex-rs/exec/tests/suite/sandbox.rs

@@ -11,7 +11,7 @@ use std::process::ExitStatus;
 use tokio::fs::create_dir_all;
 use tokio::process::Child;
 
-async fn spawn_command_under_sandbox(
+pub(super) async fn spawn_command_under_sandbox(
     command: Vec<String>,
     command_cwd: AbsolutePathBuf,
     permission_profile: &PermissionProfile,