- Add overflow/corruption guards to string (de)serialization (writer/reader now throw on invalid lengths)
- Remove dead string serialization methods per BINARY_TODO.md audit
- Update BINARY_TODO.md with closure/resolution for H2Q6, O7G2, V4N5, and related entries
- Add MaxStringCharLength constant and update marker reservations in BinaryTypeCode
- Simplify string cache ASCII verification in deserializer
- Add SGen/Runtime round-trip compatibility tests for large/deep data
- Minor code modernization and style improvements
