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/frc971/orin/cuda.cc b/frc971/orin/cuda.cc
index 89b1529..6bcc79c 100644
--- a/frc971/orin/cuda.cc
+++ b/frc971/orin/cuda.cc
@@ -7,8 +7,7 @@
     sync, false,
     "If true, force synchronization after each step to isolate errors better.");
 
-namespace frc971 {
-namespace apriltag {
+namespace frc971::apriltag {
 
 size_t overall_memory = 0;
 
@@ -25,5 +24,4 @@
   if (FLAGS_sync) CheckAndSynchronize(message);
 }
 
-}  // namespace apriltag
-}  // namespace frc971
+}  // namespace frc971::apriltag