fix: implement topology-aware cache keys with atomic epoch invalidation (Fixes #3)

[laurentketterle-hub]

Changes

Implements topology-aware cache keys for the Changefeed Deduplicator to prevent partial/dirty reads during shard rebalancing and lease handoffs.

What was done:

1. TopologyVersion struct — Added with , , and fields to track the active shard assignment configuration.
2. Topology-aware cache entries — Each now stores the under which it was recorded. Duplicate filtering is scoped to the same epoch.
3. Atomic topology updates — atomically updates the routing configuration via , providing thread-safe access from concurrent goroutines.
4. Stale cache invalidation — When the topology epoch increments, all cache entries recorded under the old epoch are automatically invalidated, preventing stale reads.
5. Cross-epoch vs same-epoch semantics — Within the same epoch, duplicate events are filtered. After a topology change (lease handoff), re-emission of events from the new shard is accepted — preventing silent data loss.

Acceptance Criteria:

• ✅ Topology-Aware Cache Keys: Cache key incorporates epoch/version
• ✅ Stale Cache Invalidation: Old-epoch entries discarded on rebalance
• ✅ Strict Error Handling: correctly distinguishes cross-epoch vs same-epoch duplicates
• ✅ Thread-Safe Routing Updates: Atomic updates via

Closes #3

Signed-off-by: laurentketterle-hub noreply@users.noreply.github.com