message: synchronizes all timers on `tic/toc`
diff: @@ -264,6 +264,7 @@ public:
  protected:
  void tic_impl() override
  {
  + exec_->synchronize();
  gko::cuda::device_guard g{id_};
  // Currently, gko::CudaExecutor always use default stream.
  GKO_ASSERT_NO_CUDA_ERRORS(cudaEventRecord(start_));
  @@ -271,6 +272,7 @@ protected:
  double toc_impl() override
  {
  + exec_->synchronize();
  gko::cuda::device_guard g{id_};
  // Currently, gko::CudaExecutor always use default stream.
  GKO_ASSERT_NO_CUDA_ERRORS(cudaEventRecord(stop_));
  @@ -330,6 +332,7 @@ public:
  protected:
  void tic_impl() override
  {
  + exec_->synchronize();
  gko::hip::device_guard g{id_};
  // Currently, gko::HipExecutor always use default stream.
  GKO_ASSERT_NO_HIP_ERRORS(hipEventRecord(start_));
  @@ -337,6 +340,7 @@ protected:
  double toc_impl() override
  {
  + exec_->synchronize();
  gko::hip::device_guard g{id_};
  // Currently, gko::HipExecutor always use default stream.
  GKO_ASSERT_NO_HIP_ERRORS(hipEventRecord(stop_));
  