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/events/simulated_event_loop_test.cc b/aos/events/simulated_event_loop_test.cc
index 23badae..050c9a3 100644
--- a/aos/events/simulated_event_loop_test.cc
+++ b/aos/events/simulated_event_loop_test.cc
@@ -19,8 +19,7 @@
 #include "aos/network/timestamp_generated.h"
 #include "aos/testing/path.h"
 
-namespace aos {
-namespace testing {
+namespace aos::testing {
 namespace {
 
 using aos::testing::ArtifactPath;
@@ -2462,5 +2461,4 @@
   }
 }
 
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing