Fixing miner issues

- Switch from full-block to header-only (140-byte) RandomX input
- Add 32-byte SoloNonce system for solo mining mode
- Compute proper difficulty target from compact bits field
- Add SHA256D dual-hash PoW check in CpuWorker for solo mining
- Raise RandomX dataset/scratchpad limits to 4GB/4MB
- Use standard RandomX share filtering in pool (stratum) mode

CMakeLists.txt

@@ -91,6 +91,7 @@ set(HEADERS_CRYPTO
     src/crypto/common/HugePagesInfo.h
     src/crypto/common/MemoryPool.h
     src/crypto/common/Nonce.h
+    src/crypto/common/SoloNonce.h
     src/crypto/common/portable/mm_malloc.h
     src/crypto/common/VirtualMemory.h
    )
@@ -128,6 +129,7 @@ set(SOURCES_CRYPTO
     src/crypto/common/HugePagesInfo.cpp
     src/crypto/common/MemoryPool.cpp
     src/crypto/common/Nonce.cpp
+    src/crypto/common/SoloNonce.cpp
     src/crypto/common/VirtualMemory.cpp
    )