Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/y2022/vision/blob_detector.cc b/y2022/vision/blob_detector.cc
index 2c6ff44..70ff1b2 100644
--- a/y2022/vision/blob_detector.cc
+++ b/y2022/vision/blob_detector.cc
@@ -25,8 +25,7 @@
              "Required difference between green pixels vs. blue when using "
              "--use_outdoors");
 
-namespace y2022 {
-namespace vision {
+namespace y2022::vision {
 
 cv::Mat BlobDetector::ThresholdImage(cv::Mat bgr_image) {
   cv::Mat binarized_image(cv::Size(bgr_image.cols, bgr_image.rows), CV_8UC1);
@@ -266,5 +265,4 @@
           << " ms";
 }
 
-}  // namespace vision
-}  // namespace y2022
+}  // namespace y2022::vision