1. Fix warnings reported by clang tidy
2. Use unique lock instead of manully lock/unlock on mutex.
The RAII style locking makes sure mutex is unlocked when exceptions are thrown
1. Utilize `m_mutex` to safeguard member fields of `hyprland::Workspaces` as they are modified by multiple threads, including the event listener thread and UI thread. This applies to all member fields, not just `m_workspacesToCreate`.
2. Tidy up the create/remove workspace code.