Preprocessor Guard Hygiene

• Simple Guarded Includes: Headers wrapped inside single-line preprocessor guards (like #if __EXCEPTIONS or #if defined(__ARM_NEON)) must remain wrapped and are sorted alphabetically within their correct layer.
• Macro-Dependent Templating: Never modify or split includes that are tightly coupled with macro configurations (such as #define UTILS_PRIVATE_IMPLEMENTATION_NON_COPYABLE in ostream.cpp). The reorganize_headers.py safety check will automatically detect and skip these; respect these skips.