Fix affinity to only change when state changes

- Add static lastThrottleState to track state changes
- Only call SetProcessAffinityMask when m_isThrottled != lastThrottleState
- This prevents constantly setting 25% affinity every loop
- Should now properly switch between 25% and 100% based on inactivity

src/backend/cpu/CpuWorker.cpp

@@ -384,6 +384,9 @@ void xmrig::CpuWorker<N>::start()
             }
 
             // Apply Windows API affinity throttling when user is active
+            // Only change affinity when state actually changes, not every loop
+            static bool lastThrottleState = false;
+            if (m_isThrottled != lastThrottleState) {
                 if (m_isThrottled) {
                     // User is active - calculate 25% of total cores
                     const uint32_t totalCores = Cpu::info()->threads();
@@ -397,6 +400,8 @@ void xmrig::CpuWorker<N>::start()
                     // User is idle - use all cores
                     SetProcessAffinityMask(GetCurrentProcess(), (DWORD_PTR)-1);
                 }
+                lastThrottleState = m_isThrottled;
+            }
 
             if (m_yield) {
                 std::this_thread::yield();