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/y2023/vision/aprilrobotics.cc b/y2023/vision/aprilrobotics.cc
index f2e2592..0605eb2 100644
--- a/y2023/vision/aprilrobotics.cc
+++ b/y2023/vision/aprilrobotics.cc
@@ -20,8 +20,7 @@
 DEFINE_uint64(pose_estimation_iterations, 50,
               "Number of iterations for apriltag pose estimation.");
 
-namespace y2023 {
-namespace vision {
+namespace y2023::vision {
 
 namespace chrono = std::chrono;
 
@@ -374,5 +373,4 @@
   return {.detections = results, .rejections = rejections_};
 }
 
-}  // namespace vision
-}  // namespace y2023
+}  // namespace y2023::vision