Fix inconsistent logic

[valzargaming]

This pull request refactors how the Discord instance is accessed throughout the bot's application command logic, introduces a create method for building Discord command objects, and moves the usage property to a more appropriate location. The main themes are code consistency, improved command construction, and minor cleanup.

Refactoring Discord Instance Access:

• Replaces direct property access ($this->discord) with a method call ($this->discord()) throughout the HasApplicationCommands concern and related command classes to standardize and encapsulate how the Discord instance is retrieved. [1] [2] [3] [4] [5] [6] [7] [8] [9]

Command Construction Improvements:

• Adds a create method to the ApplicationCommand class for building Discord command objects using CommandBuilder, ensuring consistent construction and serialization of commands.
• Updates command serialization to use jsonSerialize() instead of toArray() for compatibility and accuracy in both HasApplicationCommands and SlashCommand. [1] [2]

Code Organization and Cleanup:

• Moves the usage property from the Command class to the more general AbstractCommand class, ensuring all commands can define usage information. [1] [2]
• Adds a docblock to the HasApplicationCommands trait for clarity and documentation.

Dependency Imports:

• Adds missing imports for Discord\Discord, CommandBuilder, and Command where necessary for type safety and clarity. [1] [2]