added: sha-3(Keccak) implementation

[0xAsce]

Summary

This PR adds a SHA-3 (Keccak) hash function implementation written in Python.

Details

• Implements the SHA-3 hashing algorithm according to the Keccak specification
• Supports standard SHA-3 digest sizes (e.g. SHA3-224/256/384/512 if applicable)
• Designed to be readable and easy to audit
• No external dependencies required

Motivation

SHA-3 is a modern cryptographic hash standard and provides an alternative to SHA-2.
Adding this implementation improves the project’s cryptographic coverage and allows
users to experiment with or verify SHA-3 hashing behavior directly in Python.

Testing

• Verified outputs against known SHA-3 test vectors
• Compared results with Python’s hashlib.sha3_* for correctness

Notes

This implementation prioritizes clarity and correctness. Performance optimizations
can be explored in future iterations if needed.