Fix some concurrency warnings, update missed licence headers. (#3741)

* Switch the TimelineController to an async sequence and fix the warnings on the UserIndicatorController

ElementX/Sources/Screens/RoomScreen/ComposerToolbar/ComposerToolbarViewModelProtocol.swift

@@ -9,6 +9,7 @@ import Combine
 import WysiwygComposer
 
 // periphery: ignore - markdown protocol
+@MainActor
 protocol ComposerToolbarViewModelProtocol {
     var actions: AnyPublisher<ComposerToolbarViewModelAction, Never> { get }
     var context: ComposerToolbarViewModelType.Context { get }

ElementX/Sources/Screens/RoomScreen/RoomScreenViewModelProtocol.swift

@@ -6,8 +6,8 @@
 //
 
 import Combine
-import Foundation
 
+@MainActor
 protocol RoomScreenViewModelProtocol {
     var actions: AnyPublisher<RoomScreenViewModelAction, Never> { get }
     var context: RoomScreenViewModel.Context { get }