refactor: re-place files into correct position according to namespace hierarchy

src/yycc/rust/num/stringify.hpp

@@ -0,0 +1,10 @@
+#pragma once
+#include "../../num/stringify.hpp"
+
+namespace yycc::rust::num::stringify {
+
+    // There is no modification for legacy "stringify" functions like "parse".
+    // So we simply expose all functions into this namespace.
+    using namespace ::yycc::num::stringify;
+
+} // namespace yycc::rust::stringify