fix(schedule): prevent panicking in loop_schedule routine

[goshawk-3]

fixes #168

• We must ensure that set_server_key is always configured for every computation thread.
  It was observed that when the number of computations is only one, the comps.par_iter executes this computation in the current thread. However, since broadcast invokes are triggered only for Rayon threads, the local_storage of the current thread is not initialized with the server key.
• Additionally, to prevent blocking the Tokio executor, the Rayon execution is wrapped in spawn_blocking so .await allows us to yield.