feat(crypto): add SPHINCS+ and FALCON post-quantum algorithms
Phase 13 Milestone 2 - Enhanced Quantum Cryptography:
SPHINCS+ (FIPS 205 / SLH-DSA):
- Hash-based signatures as backup if lattice schemes are compromised
- Three variants: 128s (~7.8KB), 192s (~16KB), 256s (~30KB)
- Relies only on hash function security (conservative choice)
- SphincsKeypair, SphincsPublicKey, SphincsSecretKey, SphincsSignature
FALCON (FIPS 206 / FN-DSA):
- Compact lattice signatures for bandwidth-constrained devices
- FALCON-512: 128-bit security, ~690 byte signatures
- FALCON-1024: 256-bit security, ~1,330 byte signatures
- ~79% smaller than Dilithium3 signatures
- Ideal for mobile wallets and L2 batch transactions
Algorithm Comparison:
| Algorithm | Security | Sig Size | Use Case |
|-----------|----------|----------|----------|
| Ed25519 | 128-bit | 64 B | Classical (fast) |
| Dilithium3 | 192-bit | 3,293 B | Default PQ |
| FALCON-512 | 128-bit | 690 B | Mobile/IoT |
| SPHINCS+-128s | 128-bit | 7,856 B | Backup |
All 40 unit tests + 5 doc tests passing.
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