- Introduced `CooldownStateStore` interface for managing independent cooldown state persistence.
- Implemented `FileCooldownStateStore` for storing cooldown states as per-auth `.cds` files with atomic writes and stale file cleanup.
- Enhanced `Manager` to support restoring state from `CooldownStateStore` and persisting state changes during auth updates.
- Updated tests to validate cooldown state saving, loading, concurrency handling, and error scenarios.
Closes: #3368