High-performance log deduplication and rate limiting for the tracing ecosystem.

Features:
- Multiple rate limiting policies (count-based, time-window, exponential backoff)
- Per-signature throttling with configurable LRU eviction
- Observability metrics and circuit breaker for fail-safe operation
- 105 tests, comprehensive documentation, and CI/CD pipeline

Performance:
- 20M decisions/sec single-threaded, 44M ops/sec with 8 threads
- ~150-250 bytes per signature, default 10k signature limit

See CHANGELOG.md for full release notes.