Add should_exit support for v2 parsers

- Add should_exit support to v2 platform parsers
- Introduce macros.h and integrate trait hints
- Wire CMake packaging with config, version, and install dirs
- Update parser traits to include validation hooks and fixes

src/headers/argparse

@@ -2,6 +2,7 @@
 #ifndef ARGPARSE_HPP
 #define ARGPARSE_HPP
 #include <argument_parser.hpp>
+#include "macros.h"
 
 #ifdef __linux__
 #include <linux_parser.hpp>
@@ -37,4 +38,4 @@ namespace argument_parser::v2 {
 
 #include <base_convention.hpp>
 #include <gnu_argument_convention.hpp>
-#include <windows_argument_convention.hpp>
+#include <windows_argument_convention.hpp>