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/april_generator.cc b/y2023/vision/april_generator.cc
index 4ac389a..3746474 100644
--- a/y2023/vision/april_generator.cc
+++ b/y2023/vision/april_generator.cc
@@ -14,8 +14,7 @@
 // https://halide-lang.org/tutorials/tutorial_lesson_15_generators.html has an
 // introduction to much of the magic in this file.
 
-namespace frc971 {
-namespace vision {
+namespace frc971::vision {
 namespace {
 
 // Returns a function implementating a 1-dimensional gaussian blur convolution.
@@ -147,8 +146,7 @@
   }
 };
 
-}  // namespace vision
-}  // namespace frc971
+}  // namespace frc971::vision
 
 // TODO(austin): Combine the functions and optimize for device/host and all that
 // jazz.