Add Shutdown trigger and handle program exit

[erlingrj]

This unfortunately messes a little with gcov and we get warnings:

libgcov profiling error:/home/erling/dev/reactor-uc/build/CMakeFiles/reactor-uc.dir/src/trigger.c.gcda:overwriting an existing profile data with a different timestamp

Presumably when the shutdown reactor is executed.

[github-actions[bot]]

Coverage after merging shutdown into main will be

14.76%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
builtin_triggers.c	0%	100%	0%	0%	3–5, 7–9
connection.c	0%	0%	0%	0%	10–11, 11, 11–12, 14, 16–17, 21–22, 22, 22, 24–25, 27, 27, 27–29, 29, 29–30, 32, 34–39, 4, 40–41, 43–44, 5, 5, 5, 7, 7, 7, 7–9
environment.c	0%	100%	0%	0%	11–13, 15, 17, 19–20, 22, 25, 28–40, 8–9
logical_action.c	0%	100%	0%	0%	12–17, 4–7, 9
port.c	0%	0%	0%	0%	10, 12–16, 18–21, 23–24, 24, 24–25, 28, 28, 28–29, 31, 31, 31–33, 35, 40, 42–44, 46–47, 6–7, 7, 7–9
queues.c	55.48%	44%	66.67%	60.22%	100, 103, 109–112, 112, 112–113, 115–116, 17–18, 22–24, 24, 24–25, 30–31, 31, 31, 33–36, 36, 36, 36, 36–37, 39, 39, 39, 39, 39, 4, 40, 44, 44, 44–46, 48, 5, 50–54, 54, 54–55, 57, 6–7, 71–75, 8, 89, 94
reaction.c	0%	0%	0%	0%	11–12, 12, 12–13, 15, 19–20, 23, 23, 23–26, 26, 26–27, 32, 32, 32–34, 34, 34–35, 35, 35–36, 36, 36–38, 38, 38–40, 40, 40–43, 43, 43–44, 53, 56, 58–59, 6, 60–68, 7, 7, 7–9
reactor.c	0%	0%	0%	0%	10–11, 11, 11–13, 15–16, 16, 16–17, 19, 21, 23, 26–27, 27, 27–28, 30–31, 31, 31–32, 34, 36, 38–39, 39, 39–40, 44, 44, 44–45, 47, 49, 52–63, 7
scheduler.c	0%	0%	0%	0%	10, 12, 14, 16–17, 17, 17–18, 20, 22–23, 23, 23–25, 27, 29–33, 33, 33–35, 37–38, 40, 42–47, 47, 47–49, 49, 49, 5, 50–51, 53–54, 54, 54–55, 58–59, 6, 6, 6, 60, 62, 64–65, 65, 65–66, 68, 7, 70–71, 71, 71–72, 72, 72, 74–75, 78–79, 81–89, 9, 9, 9, 90–91
tag.c	11.58%	8.70%	20%	13.64%	21, 23, 26–27, 27, 27, 27, 27–28, 30, 30, 30, 30, 30–31, 33, 33, 33–34, 36–37, 37, 37–38, 40, 40, 40, 40, 40–41, 43, 43, 43, 43, 43–44, 46, 50–51, 53–54, 56–57, 59–60, 65–66, 66, 66, 66, 66–67, 70, 70, 70–71, 73–74, 74, 74, 78, 80–81, 83, 86–88, 88, 88, 88, 88, 88, 88, 88, 88, 88, 88–90, 92
timer.c	0%	100%	0%	0%	10, 12–13, 15, 18–20, 4, 6–8
trigger.c	0%	0%	0%	0%	10–11, 11, 11–13, 15–16, 16, 16–18, 20, 22–32, 34–37, 5–8