[FEATURE] Add CDC ChangeFeed API with resumable offsets

[feichai0017]

🚀 Is your feature request related to a problem?

There is no first-class CDC interface for downstream systems (cache invalidation, indexing, analytics pipelines). Users must poll/scans manually.

💡 Proposed Solution

Add a CDC ChangeFeed API with resumable offsets/checkpoints.

Scope:

• emit key-level mutations (put/delete/commit metadata),
• support at-least-once delivery semantics,
• support resume from persisted checkpoint.

🎨 Alternatives Considered

1. Poll data via scans.
2. Build custom tailers directly on internal logs.

Both options are less reliable and harder to maintain.

📝 Technical Details / Implementation Plan

• Define change event schema and stream API (pull or server-streaming).
• Implement checkpoint/offset persistence and restart recovery behavior.
• Add tests for ordering, duplication semantics, and backpressure handling.

🧐 Additional Context

CDC is a major integration primitive and unlocks ecosystem tooling around NoKV.