Include MONOTONIC_USEC in SystemD reload message

[Sharpie]

Short description

This commit adds the MONOTONIC_USEC field to the RELOADING message sent to SystemD. Omitting this field can cause SystemD to ignore reload messages and return from systemctl reload early.

See: https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html#Type=

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document and added a Signed-off-by annotation to each of my commits
• read and accepted the AI Policy document and added Generated-by or Assisted-by annotations to each of my commits created with the help of an AI agent
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[Sharpie]

Building openvox-server with EZbake 4.0, installing on EL 10, then removing ExecReload=kill -HUP $MAINPID from /usr/lib/systemd/system/puppetserver.service results in systemctl reload timing out as the RELOADING=1 message is ignored:

#  tail -f /var/log/puppetlabs/puppetserver/puppetserver.log
...
2026-08-30T00:15:50.493Z INFO  [async-mixed-1] [p.t.internal] Sending sd_notify message to NOTIFY_SOCKET "/run/systemd/notify": "RELOADING=1\n"
...
2026-08-30T00:15:55.371Z INFO  [async-mixed-1] [p.t.internal] Sending sd_notify message to NOTIFY_SOCKET "/run/systemd/notify": "READY=1\n"

# time systemctl reload puppetserver
Job for puppetserver.service failed.
See "systemctl status puppetserver.service" and "journalctl -xeu puppetserver.service" for details.

real    5m0.128s
user    0m0.001s
sys     0m0.006s

Re-building with this patch results in a systemctl reload that completes successfully:

#  tail -f /var/log/puppetlabs/puppetserver/puppetserver.log
...
2026-08-30T00:35:35.450Z INFO  [async-mixed-1] [p.t.internal] Sending sd_notify message to NOTIFY_SOCKET "/run/systemd/notify": "RELOADING=1\nMONOTONIC_USEC=197340680966\n"
...
2026-08-30T00:35:40.045Z INFO  [async-mixed-1] [p.t.internal] Sending sd_notify message to NOTIFY_SOCKET "/run/systemd/notify": "READY=1\n"
...

# time systemctl reload puppetserver                             00:38:47 [50/151]

real    0m4.780s
user    0m0.005s
sys     0m0.002s