clang-tidy: modernize-concat-nested-namespaces (NFC)

wpimath/src/main/native/include/units/constants.h

@@ -43,13 +43,7 @@
 #include "units/time.h"
 #include "units/velocity.h"
 
-namespace units {
-/**
- * @brief namespace for physical constants like PI and Avogadro's Number.
- * @sa See unit_t for more information on unit type containers.
- */
-#if !defined(DISABLE_PREDEFINED_UNITS)
-namespace constants {
+namespace units::constants {
 /**
  * @name Unit Containers
  * @anchor constantContainers
@@ -105,6 +99,4 @@ static constexpr const unit_t<
           (15 * math::cpow<3>(h) * math::cpow<2>(c) *
            math::cpow<4>(N_A)));  ///< Stefan-Boltzmann constant.
 /** @} */
-}  // namespace constants
-#endif
-}  // namespace units
+}  // namespace units::constants