feat!: split acknowledge config into autoAck + keepaliveIntervalSeconds (v3.0.1)

[kibae]

Summary

• Replace nested acknowledge: { auto, timeoutSeconds } with top-level autoAck and
  keepaliveIntervalSeconds. The old shape bundled two independent concerns — auto-ack on
  data messages vs. periodic keepalive — which caused the replication slot to silently
  advance past unacknowledged work when auto: false was set
  (#174).
• Track received LSN and acknowledged LSN separately internally. The keepalive timer now
  reports only the last manually acknowledged LSN as the flushed/applied position, so
  autoAck: false users can rely on the slot staying put.
• Deprecated acknowledge key is still accepted in v3.x with a console.warn and value
  mapping; scheduled for removal in v4.0.

Migration

- new LogicalReplicationService(clientConfig, {
-   acknowledge: { auto: false, timeoutSeconds: 10 },
- });
+ new LogicalReplicationService(clientConfig, {
+   autoAck: false,
+   keepaliveIntervalSeconds: 10,
+ });

Prominent notice added at the top of README.md; full details in CHANGELOG.md.

Test plan

• npx tsc --noEmit passes
• jest config-normalize — 4/4 unit tests pass (defaults, new keys, deprecated shim
  with warning, precedence when both supplied)
• Run full Jest suite against PostgreSQL 14/15/16/17/18 via CI
• Manually verify autoAck: false, keepaliveIntervalSeconds: 10 keeps connection
  alive without advancing pg_replication_slots.confirmed_flush_lsn
• Manually verify deprecated acknowledge: { auto, timeoutSeconds } still works
  with warning

Closes #174