Track compaction time in turn profiles (#34835)

## What changed

- Add `compaction_ms` to turn profile facts and turn analytics events.
- Measure manual and automatic compaction as an exclusive profile phase instead of including it in surrounding idle time.
- Complete the profile and total turn duration from the same instant so their elapsed times remain consistent.

## Testing

- Cover compaction phase accounting and profile-duration consistency.
- Update turn event serialization coverage for `compaction_ms`.

GitOrigin-RevId: 50f0e1cf19789a807f9f56c2ef763c620a5d641c

codex-rs/core/src/tasks/compact.rs

@@ -32,6 +32,7 @@ impl SessionTask for CompactTask {
         _cancellation_token: CancellationToken,
     ) -> SessionTaskResult {
         let session = session.clone_session();
+        let _profile_guard = ctx.turn_timing_state.begin_compaction();
         if ctx.config.features.enabled(Feature::TokenBudget) {
             crate::compact_token_budget::run_manual_compact_task(session, ctx).await?;
             return Ok(None);