AstroBWT 20-50% speedup

Skips hashes with large stage 2 size. Added configurable `astrobwt-max-size` parameter, default value is 550, min 400, max 1200, optimal value ranges from 500 to 600 depending on CPU.

- Intel CPUs get 20-25% speedup
- 1st- and 2nd-gen Ryzens get 30% speedup
- 3rd-gen Ryzens get up to 50% speedup

src/backend/cpu/CpuLaunchData.h

@@ -65,6 +65,7 @@ public:
     const int64_t affinity;
     const Miner *miner;
     const uint32_t intensity;
+    const int astrobwtMaxSize;
 };