message: add generic type (I give up on generated types for now)
diff: import { MessageMentions } from '../structures/messageMentions.ts'
  export type CommandArgumentMatchTypes = 'flag' | 'mention' | 'content' | 'rest'
  -export interface Args {
  +export interface Args<T = unknown> {
  name: string
  match: CommandArgumentMatchTypes
  - // Still needs to be implemented
  - // type?: unknown
  - defaultValue?: unknown
  + defaultValue?: T
  flag?: string
  }
  