Add unit tests for Utils::toHex

test/mocks/SHA256.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <stdint.h>
+#include <stddef.h>
+
+// Mock SHA256 class for testing
+// Provides minimal interface to allow Utils.cpp to compile
+class SHA256 {
+public:
+  void update(const uint8_t* data, size_t len) {}
+  void finalize(uint8_t* hash, size_t hashLen) {}
+  void resetHMAC(const uint8_t* key, size_t keyLen) {}
+  void finalizeHMAC(const uint8_t* key, size_t keyLen, uint8_t* hash, size_t hashLen) {}
+};