[F.Rq.] Alternate implementation(s) for NullEmulator.FrameAdvance

[YoshiRulz]

Currently, it sleeps for 5 ms:

BizHawk/src/BizHawk.Emulation.Common/Base Implementations/NullEmulator.cs

Lines 34 to 40 in a39689d

	public bool FrameAdvance(IController controller, bool render, bool renderSound)
	{
	// real cores wouldn't do something like this, but this just keeps speed reasonable
	// if all throttles are off
	Thread.Sleep(5);
	return true;
	}

I'm thinking it could be helpful for S–N ratio in profiling if it did something else, namely return instantly. Other options are Thread.Sleep(0) or a busy loop.

[Morilli]

I'm not sure how much use that would have for profiling because most other things aren't setup anyway, like controls are just NullController, video output is just an empty screen, no audio, no memory domains etc.

[YoshiRulz]

That's the idea. It shouldn't be allocating, and the flame graph shouldn't include any managed codepaths except the ones for sleeping.