Add RandomX hashing wrapper

src/crypto/randomx_hash.h

@@ -0,0 +1,24 @@
+#ifndef VEXTA_CRYPTO_RANDOMX_HASH_H
+#define VEXTA_CRYPTO_RANDOMX_HASH_H
+
+#include <cstddef>
+#include <cstdint>
+
+static constexpr std::size_t VEXTA_RANDOMX_HASH_SIZE = 32;
+
+/**
+ * Calculate a RandomX hash using an explicit key.
+ *
+ * This wrapper intentionally uses RANDOMX_FLAG_DEFAULT so consensus hashing
+ * does not depend on CPU-specific runtime feature detection.
+ *
+ * Returns false if RandomX cache or VM allocation fails.
+ */
+bool VextaRandomXHash(
+    const void* input,
+    std::size_t input_size,
+    const void* key,
+    std::size_t key_size,
+    uint8_t output[VEXTA_RANDOMX_HASH_SIZE]);
+
+#endif // VEXTA_CRYPTO_RANDOMX_HASH_H