Windows: CUDAEnsemble can block standby whilst running.

[Robadob]

This uses Windows API to notify that threads running models inside CUDAEnsemble don't want the PC to enter standby.

It can be disabled by setting block_standby=false or passing --standby or -s at runtime. Though I'm not sure why a user would want to do that.

I don't believe there is a similar system wide power mgmt feature on Linux.

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This requires a manual test when I have a computer spare to try it on. It may be better to add it to the parent thread temporarily, rather than to the children threads.

[ptheywood]

Looks fine, though do test it actually prevents sleep prior to merging.

[Robadob]

Looks fine, though do test it actually prevents sleep prior to merging.

Yeah will do when I don't need my PC. Tomorrow when I goto git class or weekend when I'm at the gym maybe.

[mondus]

More importantly check that the machine recovers from standby afterwards.

[Robadob]

I changed around how this was implemented (it now blocks during CUDAEnsemble::simulate() rather than the bugged call to mark every runner thread as blocking).

Have tested it works as intended. PC can still go into standby after the call to simulate() returns, even if the process is running (although it took ~2 mins rather than ~1 min that I expected).