[idd] rgb24: isolate benchmark samples from cadence

Run effect timing samples only when the retained candidate pipeline is idle
and force each completed sample to publish immediately. This prevents work
from superseded candidates from being charged to a surviving sample.

Include the indirect CPU copy to IVSHMEM in the measured copy stage while
preserving the wall-clock fallback when GPU timestamps are unavailable.

idd/LGIdd/CSwapChainProcessor.h

@@ -137,7 +137,7 @@ private:
     const CFrameScheduler::Schedule& schedule, bool periodic,
     uint64_t publishStart);
   bool HasReadyCandidate();
-  int AcquireCandidate();
+  int AcquireCandidate(bool exclusiveSample);
   void ReleaseCandidate(unsigned candidateIndex);
   bool EnsureCandidateResource(unsigned candidateIndex,
     ID3D12Resource * source);