Revaulting

Refactor Vault cooldown and reward tracking
Reworked Vault cooldown and reward handling to an event-driven model.
Introduced persistent, per-vault and per-player cooldown tracking using Persistent Data Containers, with configurable delays for normal and ominous Vaults.
Removed the global polling mechanism in favour of localised, scheduled checks near players, improving performance and thread safety.

Document configuration and declare Folia support
Added a Configuration section to the README documenting the new cooldown options and their usage.
Clarified configuration file location, time units, and value constraints.
Declared Folia support in paper-plugin.yml and bumped the plugin version to 0.4.0.