Improve open action handling for notifications

Push notifications were not opened reliably. To improve robustness, the
following changes were introduced:
1. The notification opening logic was updated to become more similar to
   URL handling, in a way that uses better defined interfaces and
   functions that provide better result guarantees, by separating
   complex handling logic, and the side-effects/mutations that
   are made after computing the open action — instead of relying on a
   complex logic function that produces side-effects as a result, which
   obfuscates the actual behavior of the function.
2. The LoadableThreadView was expanded and renamed to
   LoadableNostrEventView, to reflect that it can also handle non-thread
   nostr events, such as DMs, which is a necessity for handling push
   notifications.
3. A new type of Notify object, the `QueueableNotify` was introduced, to
   address issues where the listener/handler is not instantiated at the
   time the app notifies that there is a push notification to be opened.
   This was implemented using async streams, which simplifies the usage
   of this down to a simple "for-in" loop.

Closes: https://github.com/damus-io/damus/issues/2825
Changelog-Fixed: Fixed issue where some push notifications would not open in the app and leave users confused
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

damus/Models/URLHandler.swift

@@ -34,7 +34,7 @@ struct DamusURLHandler {
             let thread = await ThreadModel(event: nostrEvent, damus_state: damus_state)
             return .route(.Thread(thread: thread))
         case .event_reference(let event_reference):
-            return .route(.ThreadFromReference(note_reference: event_reference))
+            return .route(.LoadableNostrEvent(note_reference: event_reference))
         case .wallet_connect(let walletConnectURL):
             damus_state.wallet.new(walletConnectURL)
             return .route(.Wallet(wallet: damus_state.wallet))
@@ -99,7 +99,7 @@ struct DamusURLHandler {
         case profile(Pubkey)
         case filter(NostrFilter)
         case event(NostrEvent)
-        case event_reference(LoadableThreadModel.NoteReference)
+        case event_reference(LoadableNostrEventViewModel.NoteReference)
         case wallet_connect(WalletConnectURL)
         case script([UInt8])
         case purple(DamusPurpleURL)