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/aos/time/time_test.cc b/aos/time/time_test.cc
index d5c82f2..63a145b 100644
--- a/aos/time/time_test.cc
+++ b/aos/time/time_test.cc
@@ -8,9 +8,7 @@
 #include "aos/macros.h"
 #include "aos/util/death_test_log_implementation.h"
 
-namespace aos {
-namespace time {
-namespace testing {
+namespace aos::time::testing {
 
 namespace chrono = std::chrono;
 
@@ -226,6 +224,4 @@
   }
 }
 
-}  // namespace testing
-}  // namespace time
-}  // namespace aos
+}  // namespace aos::time::testing