Fix /qs cleanghost issues with Folia scheduler

[wling-art]

This pull request refactors the ghost shop cleaning command to improve concurrency and reliability. The main change is replacing the use of BatchBukkitExecutor with a more modern and thread-safe approach using CompletableFuture and CopyOnWriteArrayList, which better supports concurrent operations and integrates with the Folia scheduler.

Concurrency and task management improvements:

• Replaced the BatchBukkitExecutor for shop deletion tasks with a CompletableFuture-based approach, using CopyOnWriteArrayList to collect all asynchronous deletion tasks and CompletableFuture.allOf to wait for their completion. This provides better concurrency control and thread safety. [1] [2]
• Integrated the Folia scheduler by running each shop deletion task at the shop's location, ensuring compatibility with Folia's region threading model.
• Updated the completion logic to send a summary message to the user only after all deletion tasks are finished, ensuring accurate feedback.