code: def getSpanDurations(self, time_stamp, service_name, rpc_name):
      
      self.send_getSpanDurations(time_stamp, service_name, rpc_name)
      return self.recv_getSpanDurations()
docs: Given a time stamp, server service name, and rpc name, fetch all of the client services calling in paired
      with the lists of every span duration (list<i64>) from the server to client. The lists of span durations
      include information on call counts and mean/stdDev/etc of call durations.
  
      The three arguments specify epoch time in microseconds, server side service name and rpc name. The return maps
      contains the key - client_service_name and value - list<span_durations>.
  
      Parameters:
       - time_stamp
       - service_name
       - rpc_name