core/hw/rsa: Make operator bool explicit

Prevents error-prone implicit conversions to bool from occurring.

src/core/hw/rsa/rsa.h

@@ -16,7 +16,7 @@ public:
         : init(true), exponent(std::move(exponent)), modulus(std::move(modulus)) {}
     std::vector<u8> GetSignature(const std::vector<u8>& message);
 
-    operator bool() const {
+    explicit operator bool() const {
         // TODO(B3N30): Maybe check if exponent and modulus are vailid
         return init;
     }