Add xxHash32 algorithm implementation

[rodrigobnogueira]

Description

Implements the xxHash32 algorithm, an extremely fast non-cryptographic hash function designed to operate at RAM speed limits. xxHash is widely used in high-performance applications.

Changes

• Added hashes/xxhash.py with complete implementation
• Uses 4 parallel accumulators for maximum speed
• Processes data in optimized 16-byte stripes
• Carefully selected prime constants (0x9E3779B1, etc.)
• Optional seed parameter for hash variation
• 15 comprehensive doctests including:
  • Empty and small inputs
  • Large inputs
  • Edge cases (null bytes)
  • Seed functionality

Features

• Fast: One of the fastest hash algorithms
• Excellent distribution: Passes SMHasher test suite
• Production-ready: Used in Zstandard, LZ4, rsync
• Seed support: Optional seed for different hash families

Real-world Applications

• Zstandard compression (Facebook's compression algorithm)
• LZ4 compression
• rsync file synchronization
• Database indexing and deduplication
• Hash tables requiring high performance

References

• https://github.com/Cyan4973/xxHash
• https://xxhash.com/
• https://github.com/Cyan4973/xxHash/blob/dev/doc/xxhash_spec.md

Testing

• All 15 doctests pass
• Passes ruff linting
• Passes mypy type checking
• Tested with various inputs and seeds

Checklist

• [x] I have read and followed the contributing guidelines
• [x] This pull request is not a duplicate
• [x] The algorithm is implemented from scratch
• [x] The code follows the repository style
• [x] I have read CONTRIBUTING.md
• [x] This pull request is all my own work -- I have not plagiarized
• [x] I know that pull requests will not be merged if they fail the automated tests
• [x] This PR only changes one algorithm file
• [x] All new Python files are placed inside an existing directory (hashes/)
• [x] All filenames are in all lowercase characters with no spaces or dashes
• [x] All functions and variable names follow Python naming conventions
• [x] All function parameters and return values are annotated with Python type hints
• [x] All functions have doctests that pass the automated testing
• [x] All new algorithms include at least one URL that points to Wikipedia or another similar explanation