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

src/base/net/stratum/Job.h

@@ -76,7 +76,10 @@ public:
     inline const String &poolWallet() const             { return m_poolWallet; }
     inline const uint32_t *nonce() const                { return reinterpret_cast<const uint32_t*>(m_blob + nonceOffset()); }
     inline const uint8_t *blob() const                  { return m_blob; }
-    inline size_t nonceSize() const                     { return (algorithm().family() == Algorithm::KAWPOW) ?  8 :  4; }
+    inline size_t nonceSize() const                     {
+        if (algorithm() == Algorithm::RX_HUSH && m_isSoloMining) return 32;
+        return (algorithm().family() == Algorithm::KAWPOW) ?  8 :  4;
+    }
     inline size_t size() const                          { return m_size; }
     inline uint32_t *nonce()                            { return reinterpret_cast<uint32_t*>(m_blob + nonceOffset()); }
     inline uint32_t backend() const                     { return m_backend; }
@@ -96,6 +99,13 @@ public:
     inline void setHeight(uint64_t height)              { m_height = height; }
     inline void setIndex(uint8_t index)                 { m_index = index; }
     inline void setPoolWallet(const String &poolWallet) { m_poolWallet = poolWallet; }
+    inline void setTarget64(uint64_t target)            { m_target = target; m_diff = toDiff(target); }
+
+    // Solo mining support
+    inline bool isSoloMining() const                    { return m_isSoloMining; }
+    inline void setSoloMining(bool solo)                { m_isSoloMining = solo; }
+
+    void setHushHeader(const uint8_t *header108);
 
 #   ifdef XMRIG_PROXY_PROJECT
     inline char *rawBlob()                              { return m_rawBlob; }
@@ -161,6 +171,7 @@ private:
     uint64_t m_target   = 0;
     uint8_t m_blob[kMaxBlobSize]{ 0 };
     uint8_t m_index     = 0;
+    bool m_isSoloMining = false;
 
 #   ifdef XMRIG_PROXY_PROJECT
     char m_rawBlob[kMaxBlobSize * 2 + 8]{};