[codex-analytics] prevent stale guardian events from satisfying reused reviews

[rhan-oai]

Why

Reused Guardian review trunks can still have older child-turn events queued when a later review starts. The review waiter currently accepts the first terminal event it sees from the shared child session, so a stale TurnComplete can be attributed to the new review. That produces impossible analytics combinations such as non-null TTFT with sub-10 ms completion latency and zero token deltas on trunk_reused reviews.

What changed

• Preserve the child turn id returned by the Guardian review Op::UserTurn submission.
• Restrict Guardian review waiting to events correlated with that submitted child turn.
• Restrict timeout/abort draining to terminal events for the same child turn.
• Add regression coverage for stale prior-turn completions, stale prior-turn errors, and interrupt draining in codex-rs/core/src/guardian/review_session.rs.

Verification

• cargo test -p codex-core guardian::review_session::tests::
• cargo clippy -p codex-core --tests -- -D warnings

[dylan-hurd-oai]

Can we add an integration test for this?