core: clear key cache & fix private key encoding in saveInboxKeys() (#9851)

* after saving new keys, we didn't clear the cache so getInboxKeys() was still returning old keys
* remove unnecessary JSON.stringify on private key in saveInboxKeys()

Signed-off-by: 01zulfi <85733202+01zulfi@users.noreply.github.com>

packages/core/src/api/user-manager.ts

@@ -538,10 +538,11 @@ class UserManager {
         public: keys.publicKey,
         private: await this.db
           .storage()
-          .encrypt(userEncryptionKey, JSON.stringify(keys.privateKey))
+          .encrypt(userEncryptionKey, keys.privateKey)
       }
     };
     await this.updateUser(updatePayload);
+    this.keyManager.clearCache();
   }
 
   async sendVerificationEmail(newEmail?: string) {