refactor(command): refactor close command

[Akinator31]

This pull request refactors and improves the scheduled thread closure logic in both the slash and text command implementations. The main changes are the extraction of a reusable format_duration function, improved user feedback when replacing an existing scheduled closure, and a significant simplification of how category and permission information is determined and passed around. Additionally, the scheduling logic for closures has been centralized for maintainability.

User feedback improvements:

• Users are now notified with a human-readable duration when their scheduled closure replaces an existing one, using the new format_duration function for consistency.

Code simplification and maintainability:

• Category ID, category name, and permissions are now determined inline using Discord API calls, removing several helper functions and reducing duplicated code in both slash and text command paths.

Scheduling logic refactor:

• The thread closure scheduling task has been moved to a centralized schedule_one function, replacing the previous inlined and nested tokio::spawn logic, making it easier to maintain and extend.

General code improvements:

• All user-facing duration formatting now uses the new format_duration function for consistency and readability.
• Minor improvements to async message sending, reducing unnecessary variable assignments and improving code clarity.

These changes improve user experience, reduce code duplication, and make the scheduling logic easier to understand and maintain.