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/actions/action_test.cc b/aos/actions/action_test.cc
index ea46ed8..c7c3c48 100644
--- a/aos/actions/action_test.cc
+++ b/aos/actions/action_test.cc
@@ -13,10 +13,7 @@
 #include "aos/events/simulated_event_loop.h"
 #include "aos/testing/path.h"
 
-namespace aos {
-namespace common {
-namespace actions {
-namespace testing {
+namespace aos::common::actions::testing {
 
 namespace chrono = ::std::chrono;
 
@@ -515,7 +512,4 @@
   event_loop_factory_.RunFor(chrono::seconds(2));
 }
 
-}  // namespace testing
-}  // namespace actions
-}  // namespace common
-}  // namespace aos
+}  // namespace aos::common::actions::testing