Add incremental CDC retention cleanup

[Osvaldo Andrade (osvaldoandrade)]

Summary

• Replace stream retention full-changelog scans with per-record expiration pointers and bounded physical cleanup.
• Persist the changelog high-water mark so sequence numbers remain monotonic after expired records are removed.
• Keep stream read paths on persisted trim state only; FAST materialized views and PITR now depend on the retained CDC window.
• Add cleanup interval and batch-size config/Helm wiring; keep negative intervals as the explicit off switch.

Validation

• go test ./...
• git diff --check
• helm template cefas ./dist/helm/cefas