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/constants/constants_sender_test.cc b/frc971/constants/constants_sender_test.cc
index 5e551c1..e4920d3 100644
--- a/frc971/constants/constants_sender_test.cc
+++ b/frc971/constants/constants_sender_test.cc
@@ -11,8 +11,7 @@
 #include "frc971/constants/testdata/constants_data_generated.h"
 #include "frc971/constants/testdata/constants_list_generated.h"
 
-namespace frc971::constants {
-namespace testing {
+namespace frc971::constants::testing {
 
 using aos::testing::ArtifactPath;
 
@@ -121,5 +120,4 @@
       "Invalid field name");
 }
 
-}  // namespace testing
-}  // namespace frc971::constants
+}  // namespace frc971::constants::testing