constructor(item, callback) {
		this.item = item;
		/** @type {typeof QUEUED_STATE | typeof PROCESSING_STATE | typeof DONE_STATE} */
		this.state = QUEUED_STATE;
		/** @type {Callback<R> | undefined} */
		this.callback = callback;
		/** @type {Callback<R>[] | undefined} */
		this.callbacks = undefined;
		/** @type {R | null | undefined} */
		this.result = undefined;
		/** @type {WebpackError | null | undefined} */
		this.error = undefined;
	}
@param {T} item the item
@param {Callback<R>} callback the callback