Unschedule future arrivals when a source is deactivated

[Enchufa2]

This is known behaviour, yet quite unexpected and inconvenient from the user perspective:

library(simmer)

dummy <- trajectory() %>%
  log_("New arrival")

interrupt <- trajectory() %>%
  deactivate("dummy")

env <- simmer() %>%
  add_generator("dummy", dummy, function() 10) %>%
  add_generator("interrupt", interrupt, at(5)) %>%
  run()
#> 10: dummy0: New arrival

Already scheduled arrivals should be unscheduled at deactivation point.