Fixing issue described in ENG-10144#comment-16a38c06.
Tracked in ENG-10174
fetchOlmAccount creates olm.Account and returns which makes it hard to maintain and free when needed, with this approach, we use unpickleAccountAndUseCallback which handles account creation and freeing memory.
Introducing fetchPickledOlmAccount, similar to fetchOlmAccount which is going to be removed.
Depends on D14318