Modern Swift Concurrency (+actors, +tasks, -GCD, -Combine)

[Daggerpov]

Building on #279

Applying learning from:

• https://www.avanderlee.com/swift/actors/
• https://www.avanderlee.com/swift/mainactor-dispatch-main-thread/
• https://www.hackingwithswift.com/quick-start/concurrency/what-is-an-actor-and-why-does-swift-have-them

Main changes:

• Annotating entire classes with @MainActor, instead of dispatching through await MainActor.run{} or DispatchQueue.main.async
• Always using .task{} on views when possible
• Task { @MainActor in syntax instead of an internal dispatch the legacy way through GCD
• loading cached objects on disk in the background thread
• finish converting all view models to @MainActor (and make their calls async)
• Task.detached{} - > Task { @MainActor in

In progress:

• smoke testing across app to detect crashes
• Document Actors #291
• Migrate to @Observable for View Models #288 (might do in a separate PR)

WIP.