ENG-6209

On native we have e.g. crypto thread or database thread to guarantee that operations will be happen sequentially. This diff brings the same for worker (db, olm) operations. I considered having different "task queues" per message db (e.g. db or olm) but I don't think it's worth as it complicates the code a lot (based on the native code). If this turns out to be a performance problem we can consider changes.

Depends on D11275

• Test if the app still works
• Add a new dummy worker message and add await new Promise(resolve => setTimeout(resolve, 3000)); to it, so resolving it takes 3s
  • Without changes if multiple requests were scheduled then all of them resolved after ~3s one after another
  • With the changes there was a 3s delay between each of them