feat(replay): handle ReplayManager#seek before streams get registered

Streams get registered on deployment start. #seek will usually be called
within the setup step (that is, before any deployment actually start)

When this happens, save the seek argument and process it after the first
stream gets added

lib/syskit/log/replay_manager.rb

@@ -113,11 +113,12 @@ def register(deployment_task)
 
             if stream_aligner.add_streams(*new_streams)
                 _, @time = stream_aligner.step_back
+                reset_replay_base_times
             else
                 reset_replay_base_times
+                seek(@initial_seek) if @initial_seek
                 @time = stream_aligner.eof? ? end_time : start_time
             end
-            reset_replay_base_times
         end
 
         # @api private
@@ -173,6 +174,11 @@ def deregister(deployment_task)
 
         # Seek to the given time or sample index
         def seek(time_or_index)
+            if stream_aligner.empty?
+                @initial_seek = time_or_index
+                return
+            end
+
             stream_index, time = stream_aligner.seek(time_or_index, false)
             return unless stream_index