Connect to Xserve serial port

I have a variety of RS232 and UART adapters. I'd like to be able to read the Xserve's serial port for debugging when it doesn't boot properly with display output.

Also, for other future experiments...

Apple's DB9 Serial Port is used for remote console access without a KVM, but I'd also like to see if it's a standard serial port, which could be used with something like a GPS module. If so, I could build a massively-overkill (and surprisingly inefficient) NTP time server, that's more accurate than any modern Mac...

Some resources:

- [Apple's weird DB9 Pinout](https://blog.christophersmart.com/2010/11/19/using-the-serial-port-on-an-apple-xserve/)
- [Use DB9 for outgoing connections](https://www.staze.org/how-to-use-the-xserve-serial-port-for-outgoing-connections/)
- Linux on Xserve:
- Ubuntu 16.04: https://github.com/frusdelion/xserve-guides/blob/master/xserve1-1-ubuntu.md
- Old EFI GRUB Image: https://blog.christophersmart.com/2009/12/22/updated-efi-grub2-tarball-including-64bit/
- More [Serial Port / Console Port info](https://youtu.be/PTVeOkttD8A?t=539)

Information about Chrony and serial ports:

- [Chrony with PPS on DCD pin](https://chrony-project.org/examples.html#_server_using_reference_clock_on_serial_port)
- [Chronyd on Mac OS](https://www.whatroute.net/chronycontrol.html)
- [My blog post on ChronyControl and GPS on macOS](https://www.jeffgeerling.com/blog/2025/using-gps-most-accurate-time-possible-on-mac/)
- [Chronyd on Linux on Pi](https://austinsnerdythings.com/2025/02/14/revisiting-microsecond-accurate-ntp-for-raspberry-pi-with-gps-pps-in-2025/)

(Merged with #37)

No repository files, tests, or entry points are named. Start by reviewing issue #37 and the referenced Xserve serial-port and Linux resources; completion would require a defined, documented way to access the Xserve serial port and clarify whether broader serial-device experiments are in scope.

Written by the indexing model from the issue text.