[codex] extract macOS Seatbelt denial collector

[dylan-hurd-oai]

Why

The macOS Seatbelt denial collector currently lives inside the CLI debug-sandbox command, so other sandboxed execution paths cannot reuse it without duplicating process-tree and log-stream handling.

What changed

• Moves the existing collector and PID tracker into codex-sandboxing.
• Keeps the debug-sandbox command on the shared implementation.
• Waits for the macOS log stream to become ready before launching the tracked command.
• Adds bounded, process-aware retention for consumers that need a hard output cap.
• Publishes descendant PIDs as they are discovered so unrelated system denials are evicted first.

This is the reusable base for #17724; it does not expose the new command-output configuration by itself.

Validation

• cargo check -p codex-cli --tests -p codex-sandboxing
• just test -p codex-sandboxing (69 passed)

[github-actions]

Closing this pull request because it has had no updates for more than 14 days. If you plan to continue working on it, feel free to reopen or open a new PR.