refactor: Update casting templates to use std_numeric for improved type safety to resolve #17 compile problem

Author: FrozenLemonTee

src/conversion/underlying.cppm

@@ -303,42 +303,44 @@ constexpr auto numeric_risk(SrcRep value)
   return details::numeric_risk<DestRep>(value);
 }
 
-template <numeric_underlying_type DestRep, numeric_underlying_type SrcRep>
+template <std_numeric DestRep, std_numeric SrcRep>
   requires details::statically_castable<DestRep, SrcRep>
 constexpr auto unchecked_cast(SrcRep value) noexcept
     -> std::remove_cvref_t<DestRep> {
   return details::unchecked_rep_cast<DestRep>(value);
 }
 
-template <numeric_underlying_type DestRep, numeric_underlying_type SrcRep>
+template <std_numeric DestRep, std_numeric SrcRep>
   requires details::statically_castable<DestRep, SrcRep>
 constexpr auto checked_cast(SrcRep value)
     -> cast_result<std::remove_cvref_t<DestRep>> {
   return details::checked_rep_cast<DestRep>(value);
 }
 
-template <numeric_underlying_type DestRep, numeric_underlying_type SrcRep>
+template <std_numeric DestRep, std_numeric SrcRep>
   requires details::statically_castable<DestRep, SrcRep>
 constexpr auto saturating_cast(SrcRep value) noexcept
     -> std::remove_cvref_t<DestRep> {
   return details::saturating_rep_cast<DestRep>(value);
 }
 
-template <numeric_underlying_type DestRep, numeric_underlying_type SrcRep>
+template <std_numeric DestRep, std_numeric SrcRep>
   requires details::statically_castable<DestRep, SrcRep>
 constexpr auto truncating_cast(SrcRep value) noexcept
     -> std::remove_cvref_t<DestRep> {
   return details::truncating_rep_cast<DestRep>(value);
 }
 
-template <numeric_underlying_type DestRep, numeric_underlying_type SrcRep>
+template <std_numeric DestRep, std_numeric SrcRep>
   requires details::statically_castable<DestRep, SrcRep>
 constexpr auto exact_cast(SrcRep value)
     -> cast_result<std::remove_cvref_t<DestRep>> {
   return details::exact_rep_cast<DestRep>(value);
 }
 
 template <underlying_type Dest, underlying_type Src>
+  requires(!details::builtin_numeric_pair<std::remove_cv_t<Dest>,
+                                          std::remove_cv_t<Src>>)
 constexpr auto unchecked_cast(Src value) noexcept -> Dest {
   return details::cast_underlying_value<Dest>(
       value, []<typename DestRep, typename SrcRep>(SrcRep rep) {
@@ -347,6 +349,8 @@ constexpr auto unchecked_cast(Src value) noexcept -> Dest {
 }
 
 template <underlying_type Dest, underlying_type Src>
+  requires(!details::builtin_numeric_pair<std::remove_cv_t<Dest>,
+                                          std::remove_cv_t<Src>>)
 constexpr auto checked_cast(Src value) -> cast_result<Dest> {
   return details::cast_underlying_result<Dest>(
       value, []<typename DestRep, typename SrcRep>(SrcRep rep) {
@@ -355,6 +359,8 @@ constexpr auto checked_cast(Src value) -> cast_result<Dest> {
 }
 
 template <underlying_type Dest, underlying_type Src>
+  requires(!details::builtin_numeric_pair<std::remove_cv_t<Dest>,
+                                          std::remove_cv_t<Src>>)
 constexpr auto saturating_cast(Src value) noexcept -> Dest {
   return details::cast_underlying_value<Dest>(
       value, []<typename DestRep, typename SrcRep>(SrcRep rep) {
@@ -363,6 +369,8 @@ constexpr auto saturating_cast(Src value) noexcept -> Dest {
 }
 
 template <underlying_type Dest, underlying_type Src>
+  requires(!details::builtin_numeric_pair<std::remove_cv_t<Dest>,
+                                          std::remove_cv_t<Src>>)
 constexpr auto truncating_cast(Src value) noexcept -> Dest {
   return details::cast_underlying_value<Dest>(
       value, []<typename DestRep, typename SrcRep>(SrcRep rep) {
@@ -371,6 +379,8 @@ constexpr auto truncating_cast(Src value) noexcept -> Dest {
 }
 
 template <underlying_type Dest, underlying_type Src>
+  requires(!details::builtin_numeric_pair<std::remove_cv_t<Dest>,
+                                          std::remove_cv_t<Src>>)
 constexpr auto exact_cast(Src value) -> cast_result<Dest> {
   return details::cast_underlying_result<Dest>(
       value, []<typename DestRep, typename SrcRep>(SrcRep rep) {