Reuse RandomX hashing context during mining

src/crypto/randomx_hash.h

@@ -3,9 +3,31 @@
 
 #include <cstddef>
 #include <cstdint>
+#include <memory>
 
 static constexpr std::size_t VEXTA_RANDOMX_HASH_SIZE = 32;
 
+class VextaRandomXHasher
+{
+public:
+    VextaRandomXHasher(const void* key, std::size_t key_size);
+    ~VextaRandomXHasher();
+
+    VextaRandomXHasher(const VextaRandomXHasher&) = delete;
+    VextaRandomXHasher& operator=(const VextaRandomXHasher&) = delete;
+
+    bool IsValid() const;
+
+    bool Hash(
+        const void* input,
+        std::size_t input_size,
+        uint8_t output[VEXTA_RANDOMX_HASH_SIZE]);
+
+private:
+    struct Impl;
+    std::unique_ptr<Impl> m_impl;
+};
+
 /**
  * Calculate a RandomX hash using an explicit key.
  *