Concurrency Fixes (#283)

* Review places where MainActor used

* Adapt to MainActor changes, avoid redundant task detachments

* Move Rust client operations into a dedicated concurrent queue, make init async

* Add changelog

* Fixed small working for awaiting non-async method

* Remove some redundant tasks

* Put back some main actors

* Fix tests

* Fixed timeline updates when the number of items doesn't change. Keeps more previous home screen room data between reloads

Co-authored-by: Stefan Ceriu <stefanc@matrix.org>

ElementX/Sources/Services/Background/BackgroundTaskServiceProtocol.swift

@@ -16,6 +16,7 @@
 
 import Foundation
 
+@MainActor
 protocol BackgroundTaskServiceProtocol {
     func startBackgroundTask(withName name: String,
                              isReusable: Bool,