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/target_mapping.cc b/y2023/vision/target_mapping.cc
index 83705b9..af4c36c 100644
--- a/y2023/vision/target_mapping.cc
+++ b/y2023/vision/target_mapping.cc
@@ -58,8 +58,7 @@
 DECLARE_int32(max_target_id);
 DECLARE_bool(visualize_solver);
 
-namespace y2023 {
-namespace vision {
+namespace y2023::vision {
 using frc971::vision::DataAdapter;
 using frc971::vision::ImageCallback;
 using frc971::vision::PoseUtils;
@@ -430,8 +429,7 @@
   mapper_replay.MaybeSolve();
 }
 
-}  // namespace vision
-}  // namespace y2023
+}  // namespace y2023::vision
 
 int main(int argc, char **argv) {
   aos::InitGoogle(&argc, &argv);