[codex] route sleep through time providers (#29973)

## Summary

- add a cancellable sleep operation to `TimeProvider`
- route `clock.sleep` through the configured provider
- extend the supported sleep duration to 12 hours
- complete the sleep turn item before propagating provider failures

## Why

This isolates the core clock abstraction needed by external clock
integrations. Existing system and app-server behavior remains wall-clock
based in this PR; the stacked follow-up supplies app-server sleeps from
an external clock.

codex-rs/app-server/src/current_time.rs

@@ -10,6 +10,7 @@ use chrono::Utc;
 use codex_app_server_protocol::CurrentTimeReadParams;
 use codex_app_server_protocol::CurrentTimeReadResponse;
 use codex_app_server_protocol::ServerRequestPayload;
+use codex_core::SleepFuture;
 use codex_core::TimeFuture;
 use codex_core::TimeProvider;
 use codex_protocol::ThreadId;
@@ -49,6 +50,13 @@ impl TimeProvider for AppServerTimeProvider {
             request_current_time(outgoing, thread_state_manager, thread_id).await
         })
     }
+
+    fn sleep(&self, _thread_id: ThreadId, duration: Duration) -> SleepFuture<'_> {
+        Box::pin(async move {
+            tokio::time::sleep(duration).await;
+            Ok(())
+        })
+    }
 }
 
 async fn request_current_time(