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

Testing

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

Checklist

• Code follows project style guidelines
• Type hints included
• Doctests included and passing
• English documentation with references
• No external dependencies