✨ Add useExisting option to LockManager.acquire

[flovouin]

📝 Description of the PR

This PR adds the useExisting option to LockManager.acquire to reuse an existing released lock entity. When true and a released (or expired) lock exists, only lock and expiresAt are updated, preserving other fields. When false (default) or no lock exists, it creates a new lock as before.

📋 Check list

• 🧪 Unit tests have been written.
• 📝 Documentation has been updated.