async save(mention) {
        if (this.#ids[mention.id.toHexString()]) {
            const existing = this.#store.findIndex((item) => {
                return item.id.equals(mention.id);
            });
            this.#store.splice(existing, 1, mention);
        } else {
            this.#store.push(mention);
            this.#ids[mention.id.toHexString()] = true;
        }
    }
@param {Mention} mention
@returns {Promise<void>}