message: Make ExecutionContext::Guard non-copyable/non-movable
diff: @@ -18,6 +18,11 @@ class ExecutionContext
  ExecutionContext& m_execution_context; ///< Reference to the guarded execution context.
  public:
  + Guard(const Guard&) = delete;
  + Guard(Guard&&) = delete;
  + Guard& operator=(const Guard&) = delete;
  + Guard& operator=(Guard&&) = delete;
  +
  explicit Guard(ExecutionContext& ctx) noexcept : m_execution_context{ctx}
  {
  ++m_execution_context.depth;
  