Enhance README with usage examples and features

Added usage examples and improved feature descriptions in README.

verify mutation; zero leaks

added end-to-end verification for the sbox logic. 
confirmed block-cipher mutation and plaintext recovery 
using the materialization engine.

Verified:
- Payload shredding to blocks
- High-entropy transit state
- Zero leak materialization

valgrind:
- All heap blocks were freed -- no leaks are possible