Crashes within agents run with create_agent_runner_fixture cause tests to hang

[BrianJKoopman]

This was seen in a recent socs PR: simonsobs/socs#686

A crash within the Agent doesn't bring the agent down, but hold up the tests, hanging until killed either by the user or by GitHub Actions after 6 hours.

A configurable timeout should be added that'll raise an error for the given test and move on. This should be possible with subprocess.run() in place of subprocess.Popen().