[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/protocol/src/items.rs

@@ -47,6 +47,7 @@ pub enum TurnItem {
     Reasoning(ReasoningItem),
     WebSearch(WebSearchItem),
     ImageView(ImageViewItem),
+    Sleep(SleepItem),
     ImageGeneration(ImageGenerationItem),
     FileChange(FileChangeItem),
     McpToolCall(McpToolCallItem),
@@ -140,6 +141,12 @@ pub struct ImageViewItem {
     pub path: AbsolutePathBuf,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema, PartialEq, Eq)]
+pub struct SleepItem {
+    pub id: String,
+    pub duration_ms: u64,
+}
+
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema, PartialEq)]
 pub struct ImageGenerationItem {
     pub id: String,
@@ -576,6 +583,7 @@ impl TurnItem {
             TurnItem::Reasoning(item) => item.id.clone(),
             TurnItem::WebSearch(item) => item.id.clone(),
             TurnItem::ImageView(item) => item.id.clone(),
+            TurnItem::Sleep(item) => item.id.clone(),
             TurnItem::ImageGeneration(item) => item.id.clone(),
             TurnItem::FileChange(item) => item.id.clone(),
             TurnItem::McpToolCall(item) => item.id.clone(),
@@ -596,6 +604,7 @@ impl TurnItem {
                     path: item.path.clone(),
                 })]
             }
+            TurnItem::Sleep(_) => Vec::new(),
             TurnItem::ImageGeneration(item) => vec![item.as_legacy_event()],
             TurnItem::FileChange(item) => item
                 .as_legacy_end_event(String::new())