Scheduler worker tasks and remote sandbox requests can block indefinitely on unresponsive HTTP calls

[zhongwen666]

Problem

Two HTTP call sites lack timeouts and can hang indefinitely when a worker or remote sandbox server becomes unresponsive:

1. BaseTask.run_on_worker in rock/admin/scheduler/task_base.py is awaited without any timeout inside the scheduler's bounded-concurrency runner. A single stuck worker holds its semaphore slot forever, starving the scheduler.
2. RemoteSandboxRuntime._request in rock/sandbox/remote_sandbox.py issues requests.post without a timeout, so a hung server blocks the calling thread indefinitely.

Impact

Stuck workers/servers can wedge the admin scheduler and SDK callers, with no recovery until the process is restarted.

Expected

Both call sites should enforce a timeout and surface the failure instead of blocking forever.