ref(e2ee) change jsdoc return to correct promise

the editor will no longer complain about superfluous await when calling these functions

modules/e2ee/crypto-utils.js

  * Ratchets a key. See
  * https://tools.ietf.org/html/draft-omara-sframe-00#section-4.3.5.1
  * @param {CryptoKey} material - base key material
- * @returns {ArrayBuffer} - ratcheted key material
+ * @returns {Promise<ArrayBuffer>} - ratcheted key material
  */
 export async function ratchet(material) {
     const textEncoder = new TextEncoder();
  * suitable for our usage.
  * @param {ArrayBuffer} keyBytes - raw key
  * @param {Array} keyUsages - key usages, see importKey documentation
- * @returns {CryptoKey} - the WebCrypto key.
+ * @returns {Promise<CryptoKey>} - the WebCrypto key.
  */
 export async function importKey(keyBytes) {
     // https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/importKey