v0.2.0

release: bump version to 0.2.0

Key changes since 0.1.0:
- HLC: packed single-atomic (fixes concurrency bug, 20x batch speedup)
- Quorum durability: fsync after each Raft batch (crash-safe writes)
- Read-your-writes: process_command(reply_from: :local) for ACID
- Compound key format for lists/hash/set through Raft
- Test stability: unique keys, eventually, cascade prevention
- CI: partition tests excluded from core, included in cluster job

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>