Fix timeout priority

[Enchufa2]

The execution priority for timeout activities has been set to PRIORITY_MIN, which should have been always the case. #228 and this fix enable custom service priority implementations with the help of renege_if and set_prioritization, e.g.:

env <- simmer()

custom <- trajectory() %>%
  set_attribute("arrival time", function() now(env)) %>%
  renege_if(
    "recompute priority",
    out = trajectory() %>%
      # e.g., increase priority if wait_time < 3
      set_prioritization(function() {
        if (now(env) - get_attribute(env, "arrival time") < 3)
          c(1, NA, NA)     # only change the priority
        else c(NA, NA, NA) # don't change anything
      }, mod="+") %>%
      # go 2 steps back to renege_if
      rollback(2)) %>%
  seize("resource") %>%
  renege_abort() %>%
  log_("processing") %>%
  timeout(5) %>%
  # trigger this before releasing the resource
  send("recompute priority") %>%
  timeout(0) %>%
  release("resource")

env %>%
  add_resource("resource") %>%
  add_generator("dummy", custom, at(0:4)) %>%
  run() %>% invisible()
#> 0: dummy0: processing
#> 5: dummy3: processing
#> 10: dummy4: processing
#> 15: dummy1: processing
#> 20: dummy2: processing

This example has been included in the "Queueing systems" vignette, and applies to cases such as this and #226.

[codecov]

Codecov Report

Merging #229 into master will not change coverage by %.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #229   +/-   ##
=======================================
  Coverage   99.74%   99.74%           
=======================================
  Files          46       46           
  Lines        2791     2791           
=======================================
  Hits         2784     2784           
  Misses          7        7           

Impacted Files	Coverage Δ
inst/include/simmer/activity/timeout.h	100.00% <100.00%> (ø)

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