Maintenance mode should free resources

[tazlin]

There are a couple of possible approaches to this:

1. The worker simply instructs all ComfyUI processes to unload models using the usual mechanisms (UNLOAD_MODELS_FROM_RAM message).
   • This has the side effect of retaining ~200mb of RAM per process
   • The safety process does not currently have an unload mechanism. Either one would be need to be implemented, or the safety process could alternatively be stopped - which would require the worker not attempt to automatically restart it as is currently the case.
2. The worker shuts down all sub-processes, including the safety process.
   • It may be sufficient to shut all but one inference process and unload it's models, which would reduce ramp up time once maintenance mode is cleared.
   • Again, the worker would need a flag to avoid reloading these halted processes once they are halted for maintenance.