util: Require integers for SaturatingAdd() and AdditionOverflow()

Previously we could fall back to using an unspecialized implementation of std::numeric_limits<T> which would compile as long as the numeric operators existed, but would return 0 for min() & max().

src/util/overflow.h

@@ -13,10 +13,9 @@
 #include <optional>
 #include <type_traits>
 
-template <class T>
+template <std::integral T>
 [[nodiscard]] bool AdditionOverflow(const T i, const T j) noexcept
 {
-    static_assert(std::is_integral_v<T>, "Integral required.");
     if constexpr (std::numeric_limits<T>::is_signed) {
         return (i > 0 && j > std::numeric_limits<T>::max() - i) ||
                (i < 0 && j < std::numeric_limits<T>::min() - i);
@@ -41,7 +40,7 @@ template <std::unsigned_integral T, std::unsigned_integral U>
     return true;
 }
 
-template <class T>
+template <std::integral T>
 [[nodiscard]] T SaturatingAdd(const T i, const T j) noexcept
 {
     if constexpr (std::numeric_limits<T>::is_signed) {