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/wpilib/fpga_time_conversion.cc b/frc971/wpilib/fpga_time_conversion.cc
index 6f9a267..3ca9984 100644
--- a/frc971/wpilib/fpga_time_conversion.cc
+++ b/frc971/wpilib/fpga_time_conversion.cc
@@ -2,8 +2,7 @@
 
 #include "aos/util/compiler_memory_barrier.h"
 
-namespace frc971 {
-namespace wpilib {
+namespace frc971::wpilib {
 
 std::optional<std::chrono::nanoseconds> CalculateFpgaOffset() {
   aos_compiler_memory_barrier();
@@ -32,5 +31,4 @@
   return monotonic_now.time_since_epoch() - fpga_average;
 }
 
-}  // namespace wpilib
-}  // namespace frc971
+}  // namespace frc971::wpilib