More precise hashrate calculation

- Use only steady timestamp counters to guarantee correctness
- CPU backend: directly measure total hashrate using raw hash counters from each thread; update data more often on ARM CPUs because they're slower
- GPU backends: directly measure total hashrate too, but use interpolator with 4 second lag to fix variance from batches of hashes

Total hashrate is now measured directly (realtime for CPU, 4 seconds lag for GPU), so it might differ a bit from the sum of all thread hashrates because data points are taken at different moments in time.

Overhead is reduced a lot since it doesn't have to go through all threads to calculate max total hashrate on every timer tick (2 times a second).

src/backend/opencl/OclWorker.h

@@ -27,6 +27,7 @@
 #define XMRIG_OCLWORKER_H
 
 
+#include "backend/common/HashrateInterpolator.h"
 #include "backend/common/Worker.h"
 #include "backend/common/WorkerJob.h"
 #include "backend/opencl/OclLaunchData.h"
@@ -50,6 +51,7 @@ public:
 
     ~OclWorker() override;
 
+    uint64_t rawHashes() const override;
     void jobEarlyNotification(const Job&) override;
 
     static std::atomic<bool> ready;
@@ -70,6 +72,8 @@ private:
     OclSharedData &m_sharedData;
     WorkerJob<1> m_job;
     uint32_t m_deviceIndex;
+
+    HashrateInterpolator m_hashrateData;
 };