Remove Boost filesystem support

Removed conditional inclusion of Boost filesystem in favor of using the standard filesystem unconditionally. Simplifies the codebase by removing dependencies and relying solely on the standard library features.

platform/include/roughpy/platform/filesystem.h

@@ -28,24 +28,14 @@
 #ifndef ROUGHPY_PLATFORM_FILESYSTEM_H_
 #define ROUGHPY_PLATFORM_FILESYSTEM_H_
 
-#include "available_libraries.h"
 #include "serialization.h"
 
-
-#if defined(RPY_HAS_STD_FILESYSTEM) && RPY_HAS_STD_FILESYSTEM
 #  include <filesystem>
-#else
-#  include <boost/filesystem.hpp>
-#endif
 
 namespace rpy {
 namespace fs {
 
-#if defined(RPY_HAS_STD_FILESYSTEM) && RPY_HAS_STD_FILESYSTEM
 using namespace std::filesystem;
-#else
-using namespace boost::filesystem;
-#endif
 
 
 template <typename Archive>