Update pqs_core.py

PQS v1.2

- Replaced custom Cube A+B hash with PBKDF2-HMAC-SHA256 (200k iterations, configurable via PQS_KDF_ITERS).
- Added key separation (BLAKE2s) for encryption and MAC.
- Implemented data authentication via BLAKE2s-MAC (16-byte tag).
- Introduced streaming keystream generator instead of short-key XOR.
- Redesigned block structure: VERSION + salt + kdf_iters + padded(tag + orig_size + ciphertext).
- Removed old check/auth embed_integrity().
- Kept fakepad obfuscation but migrated padding generation to new pqs_hash (ARX sponge scheme).
- Added iteration count control and storage in header for compatibility :))

Update README.md

:))

README.md