test: cover startup recovery for inactive invalidated slot

[psteinroe]

Summary

• add a dedicated slot recovery integration test for startup when the replication slot is already inactive and invalidated
• assert active = false before startup and wal_status = 'lost' before restart to cover the exact inactive-at-start condition
• verify startup surfaces a slot invalidation error and then recovery drops the invalidated inactive slot

Testing

• cargo test --features test-utils --test slot_recovery_tests -- --nocapture