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.cpp

@@ -186,6 +186,14 @@ size_t xmrig::Job::nonceOffset() const
 }
 
 
+void xmrig::Job::setHushHeader(const uint8_t *header108)
+{
+    memset(m_blob, 0, sizeof(m_blob));
+    memcpy(m_blob, header108, 108);
+    m_size = 140;  // 108 + 32-byte nonce space
+}
+
+
 void xmrig::Job::setDiff(uint64_t diff)
 {
     m_diff   = diff;