ppsspp-0004: sceKernelLockMutex/CB and sceKernelLockLwMutex/CB (4 sites)
scan mutex->waitingThreads vector with std::find before push_back --
O(W) per lock attempt. Fix: parallel unordered_set for O(1) dedup.
Unit test extended to cover ppsspp-0004; all 8/8 PASS (ratios 5-27x).
