Refactor opsqueue_service to use wait_for_server for port assignment and add utility function for server wait logic

[ReinierMaas]

Refactor opsqueue_service to use wait_for_server for port assignment and add utility function for server wait logic.

[Copilot]

Pull request overview

This PR refactors the test infrastructure to dynamically detect server ports rather than pre-assigning them. The main change introduces a wait_for_server utility function that monitors a process until it starts listening on a port, eliminating the need for the previous random_free_port() approach.

Key Changes:

• Added a new wait_for_server() utility function that polls a process using psutil to detect when it starts listening on a port
• Modified opsqueue_service() to use psutil.Popen instead of subprocess.Popen and dynamically discover the server port via wait_for_server()
• Changed the default port parameter from None to 0, which allows the OS to assign an available port that is then discovered

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
libs/opsqueue_python/tests/util.py	New utility module containing wait_for_server() function with retry logic to wait for a process to start listening on a port
libs/opsqueue_python/tests/conftest.py	Updated opsqueue_service() to use psutil.Popen and call wait_for_server() for dynamic port discovery instead of pre-assigning ports

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[ReinierMaas]

Locally I can reproduce the following error (and I haven't got the time to look into opsqueue testing further today):

$ just test-integration
...
ImportError while loading conftest '/home/reinier/channable/opsqueue/libs/opsqueue_python/tests/conftest.py'.
tests/conftest.py:18: in <module>
    from tests.util import wait_for_server
tests/util.py:5: in <module>
    from psutil._common import pconn
E   ImportError: cannot import name 'pconn' from 'psutil._common' (/home/reinier/channable/opsqueue/libs/opsqueue_python/.venv-f18c27186ba748256260726c822c1d608abd1229/lib/python3.12/site-packages/psutil/_common.py)
error: Recipe `test-integration` failed with exit code 4

Maybe we need to update the nixpkgs pin to make this work?