Reuse local notification logic with push notifications

Testing
-------

Conditional pass

Device: iPhone 15 Pro simulator
iOS: 17.0.1
Damus: This commit
Coverage:

1. Mention notification works (local and push). PASS

2. Thread replies do not appear (but upon code inspection it seems like
   it was not supported before). PASS?

3. DM notification works with decryption (local and push). PASS

4. Zaps not yet implemented. Coming later.

Closes: https://github.com/damus-io/damus/issues/1702
Closes: https://github.com/damus-io/damus/issues/1703
Changelog-Changed: Improve push notification support to match local notification support
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
Signed-off-by: William Casarin <jb55@jb55.com>

DamusNotificationService/NotificationExtensionState.swift

@@ -0,0 +1,29 @@
+//
+//  NotificationExtensionState.swift
+//  DamusNotificationService
+//
+//  Created by Daniel D’Aquino on 2023-11-27.
+//
+
+import Foundation
+
+struct NotificationExtensionState: HeadlessDamusState {
+    let ndb: Ndb
+    let settings: UserSettingsStore
+    let contacts: Contacts
+    let muted_threads: MutedThreadsManager
+    let keypair: Keypair
+    let profiles: Profiles
+    
+    init?() {
+        guard let ndb = try? Ndb(owns_db_file: false) else { return nil }
+        self.ndb = ndb
+        self.settings = UserSettingsStore()
+        
+        guard let keypair = get_saved_keypair() else { return nil }
+        self.contacts = Contacts(our_pubkey: keypair.pubkey)
+        self.muted_threads = MutedThreadsManager(keypair: keypair)
+        self.keypair = keypair
+        self.profiles = Profiles(ndb: ndb)
+    }
+}