fix is_tuple namespace location

Author: SteveBronder

test/unit/math/mix/util.hpp

@@ -30,7 +30,7 @@ inline double get_val(T&& x) {
  */
 template <typename F, typename... Types>
 inline void recursive_for_each(F&& f, Types&&... args) {
-  if constexpr (std::conjunction_v<stan::math::is_tuple<Types>...>) {
+  if constexpr (std::conjunction_v<stan::is_tuple<Types>...>) {
     stan::math::for_each(
         [&f](auto&&... args_i) { recursive_for_each(f, args_i...); }, args...);
   } else {

test/unit/math/prim/meta/is_tuple_test.cpp

@@ -4,9 +4,9 @@
 #include <vector>
 
 TEST(MathMetaPrim, is_tuple) {
-  EXPECT_TRUE((stan::math::is_tuple<std::tuple<double>>::value));
-  EXPECT_TRUE((stan::math::is_tuple<std::tuple<double>&>::value));
-  EXPECT_TRUE((stan::math::is_tuple<std::tuple<double>&&>::value));
-  EXPECT_FALSE((stan::math::is_tuple<double>::value));
-  EXPECT_FALSE((stan::math::is_tuple<std::vector<double>>::value));
+  EXPECT_TRUE((stan::is_tuple<std::tuple<double>>::value));
+  EXPECT_TRUE((stan::is_tuple<std::tuple<double>&>::value));
+  EXPECT_TRUE((stan::is_tuple<std::tuple<double>&&>::value));
+  EXPECT_FALSE((stan::is_tuple<double>::value));
+  EXPECT_FALSE((stan::is_tuple<std::vector<double>>::value));
 }