- Add #include <type_traits> to both .cpp and .h for static_asserts
- Clarify CompactString comment: explicitly note it is not trivially
copyable, and that memcpy safety relies on validated layout property
- Use memcpy_fn indirection to suppress both GCC -Wclass-memaccess
and clang-tidy bugprone-undefined-memory-manipulation without
platform-specific pragma guards