Implement MarketMetadataSync class for background synchronization of
market metadata with Redis-based caching. Key features:
- MarketMetadata dataclass with derived category field
- Automatic category derivation from market title (politics, crypto,
sports, entertainment, finance, tech, science, other)
- Background sync loop with configurable interval (default: 5 min)
- Redis caching with TTL-based expiration (default: 10 min)
- Cache-first lookups via get_market() method
- State management with callbacks for monitoring
- Comprehensive test suite (29 tests)
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
