add Composer decorator

[Hambay]

The Composer decorator is needed for cases when it is necessary to process events regardless of the scene.

like this.

@Composer()
export class CoreComposer {
  constructor(private userService: UserService) {}

  @Start()
  async start(@Ctx() ctx: TelegramContext) {
    if (ctx.user?.isAuthenticated) {
      return ctx.scene.enter(SceneToken.WELCOME);
    } else {
      return ctx.scene.enter(SceneToken.USERNAME_INPUT);
    }
  }

  @Command('exit')
  async exit(@Ctx() ctx: TelegramContext) {
    if (ctx.user) {
      this.userService.deauthenticateUser(ctx.user.id);
    }
    ctx.session = undefined;
    return ctx.scene.enter(SceneToken.WELCOME);
  }
}

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