SHA3-09 ParallelHash and ParallelHashXOF

[turkananation]

SHA3-09 ParallelHash and ParallelHashXOF

Summary

Implement ParallelHash128, ParallelHash256, ParallelHashXOF128, and
ParallelHashXOF256.

Scope

• Implement sequential ParallelHash first.
• Validate block-size B.
• Add NIST ParallelHash and ParallelHashXOF examples.
• Add multi-block tests and benchmark before making performance claims.

Acceptance criteria

• NIST ParallelHash vectors pass.
• Multi-block inputs exercise the transcript shape.
• blockSize <= 0 is rejected.
• Docs do not claim speedups until benchmarks justify them.

References

• doc/FIPS202_SP800185_RELEASE_GUIDE.md - ParallelHash and ParallelHashXOF
• SP 800-185 Sections 6 and 7.3

Priority: P1