Start runs faster on stations

Between two runs on a station, the next run only started after its Python workers had spawned and each plug had started in turn, so an operator clicking Run again waited on work that could have overlapped.

• Improved run start: the worker pool now spawns while the unit is identified and the plugs start, and plugs of the same scope start together instead of one after another
• Measured on a demo station: Run again to the first prompt went from about 500 ms to 300-420 ms, and a cold start with three plugs from about 1.1 s to 0.7 s
• Fixed a worker that cannot start being reported as a phase error instead of a run initialization error