provide "lag" info in switching station digiline response

technic/machines/switching_station.lua

@@ -85,7 +85,8 @@ minetest.register_node("technic:switching_station",{
 				end
 				digilines.receptor_send(pos, technic.digilines.rules, channel, {
 					supply = meta:get_int("supply"),
-					demand = meta:get_int("demand")
+					demand = meta:get_int("demand"),
+					lag = meta:get_int("lag")
 				})
 			end
 		},

technic/machines/switching_station_globalstep.lua

@@ -103,6 +103,9 @@ minetest.register_globalstep(function(dtime)
 
 				local meta = minetest.get_meta(pos)
 
+				-- set lag in microseconds into the "lag" meta field
+				meta:set_int("lag", switch_diff)
+
 				-- overload detection
 				if switch_diff > 250000 then
 					switch.skip = 30