fix: add support for mongodb@6

Reference: https://github.com/mongodb/node-mongodb-native/blob/HEAD/etc/notes/CHANGES_6.0.0.md#findoneandx-family-of-methods-will-now-return-only-the-found-document-or-null-by-default-includeresultmetadata-is-false-by-default

lib/index.ts

@@ -6,7 +6,7 @@ import {
   Session,
 } from "socket.io-adapter";
 import { randomBytes } from "crypto";
-import { ObjectId, MongoServerError } from "mongodb";
+import { ObjectId, MongoServerError, WithId, Document } from "mongodb";
 import type { Collection, ChangeStream, ResumeToken } from "mongodb";
 
 const randomId = () => randomBytes(8).toString("hex");
@@ -821,11 +821,15 @@ export class MongoAdapter extends Adapter {
       return Promise.reject("error while fetching session");
     }
 
-    if (!results[0].value || !results[1]) {
+    const result = (results[0].ok
+      ? results[0].value // mongodb@5
+      : results[0]) as unknown as WithId<Document>; // mongodb@6 (https://github.com/mongodb/node-mongodb-native/blob/HEAD/etc/notes/CHANGES_6.0.0.md#findoneandx-family-of-methods-will-now-return-only-the-found-document-or-null-by-default-includeresultmetadata-is-false-by-default)
+
+    if (!result || !results[1]) {
       return Promise.reject("session or offset not found");
     }
 
-    const session = results[0].value.data;
+    const session = result.data;
 
     // could use a sparse index on [_id, nsp, data.opts.rooms, data.opts.except] (only index the documents whose type is EventType.BROADCAST)
     const cursor = this.mongoCollection.find({