Connections as trigger and a comprehensive restructuring

[erlingrj]

• Redesign of the Trigger type hierarchy
• Connections are now Triggers. This is a good abstraction for Delayed, Physical and Federated connections.

[erlingrj]

Self-review looks good.

[github-actions]

Coverage after merging conn-as-trigger into main will be

88.81%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
action.c	85.87%	56.25%	100%	91.30%	12, 49–50, 53, 57, 61, 64, 83–84, 87, 91, 94, 97
builtin_triggers.c	93.48%	75%	100%	97.06%	12, 19–20
connection.c	70.37%	55.17%	69.23%	75.27%	10, 10, 104, 109, 13, 131, 134, 14, 14, 14, 149, 15, 150–154, 156–157, 161, 165, 168, 17, 171–172, 175–176, 19–20, 25, 38, 40, 45, 50–51, 8
environment.c	91.94%	100%	77.78%	93.88%	40, 45–46
port.c	92.59%	60%	100%	100%	14, 23–24, 8
queues.c	92.45%	80.77%	100%	97.89%	101, 17, 31, 40–41, 72–76, 90, 95
reaction.c	91.53%	80%	100%	97.22%	22–23, 34–35, 40
reactor.c	75%	50%	100%	80%	14, 19–20, 20, 20–21, 23, 35, 38–39, 39, 39–40, 42
scheduler.c	92.90%	81.48%	100%	97.46%	114–116, 14, 33, 6–7, 72, 75, 77, 85, 90, 98
tag.c	33.68%	26.09%	40%	40.91%	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, 56–57, 59–60, 66, 70–71, 86–88, 88, 88, 88, 88, 88, 88, 88, 88, 88, 88–90, 92
timer.c	97.14%	75%	100%	100%	40
trigger.c	91.67%	75%	100%	94.44%	13, 9
trigger_value.c	91.30%	80%	100%	93.75%	17–18, 8–9
src/platform
posix.c	78.08%	42.86%	90.91%	85.42%	24, 29–30, 39, 41, 41, 41–42, 44, 54–56, 64, 70, 76