[codex] Add interruptible sleep tool (#28429)

## Why

Models sometimes need to pause briefly while waiting for external work,
but using a shell command for that delay ties the wait to a process and
does not naturally resume when new turn input arrives.

## What changed

- add a built-in `sleep` tool behind the under-development `sleep_tool`
feature
- accept a bounded `duration_ms` argument, matching the millisecond
convention used by unified exec
- end the sleep early when either steered user input or mailbox input
arrives
- include elapsed wall-clock time in completed and interrupted outputs
- emit a dedicated core `SleepItem` through `item/started` and
`item/completed`
- expose the sleep item as app-server v2 `ThreadItem::Sleep` and retain
it in reconstructed thread history
- regenerate the configuration schema for the new feature flag
- regenerate app-server JSON and TypeScript schema fixtures

## Test plan

- `just test -p codex-core sleep_tool_follows_feature_gate`
- `just test -p codex-core any_new_input_interrupts_sleep`
- `just test -p codex-app-server-protocol`
- `just test -p codex-app-server
sleep_emits_started_and_completed_items`

codex-rs/rollout/src/policy.rs

@@ -95,10 +95,14 @@ pub fn should_persist_event_msg(ev: &EventMsg) -> bool {
         | EventMsg::ImageGenerationEnd(_)
         | EventMsg::SubAgentActivity(_) => true,
         EventMsg::ItemCompleted(event) => {
-            // Plan items are derived from streaming tags and are not part of the
-            // raw ResponseItem history, so we persist their completion to replay
-            // them on resume without bloating rollouts with every item lifecycle.
-            matches!(event.item, codex_protocol::items::TurnItem::Plan(_))
+            // These items have no equivalent raw ResponseItem or legacy event,
+            // so persist their completion for replay without retaining every
+            // item lifecycle event.
+            matches!(
+                event.item,
+                codex_protocol::items::TurnItem::Plan(_)
+                    | codex_protocol::items::TurnItem::Sleep(_)
+            )
         }
         EventMsg::Error(_)
         | EventMsg::GuardianAssessment(_)