Add initial ZMQ simulator for pixelator based on docuemntation

[Thomas Hopkins (thopkins32)]

Assisted-by: oh-my-pi:gpt-6-sol

TODO

• Validate correctness against real ZMQ server
• Check how the file writing actually works
  • Are ZMQ SUB updates indicative of file writing progress? (doubt it...)
• Depending on the above, it determines how we will emit documents from the ophyd-async device
  • If we can reliable file writing progress indicators, then we can declare stream early and emit StreamDatum during a flyscan
  • If we don't have it, then we must declare stream and then emit one bulk StreamDatum, all after complete().