Implement zap notification support for push notifications

The code paths for generating zap notifications were very different from
the paths used by most other notifications. In this commit, I include
the logic and data structures necessary for formatting zap notifications
in the same fashion as local notifications.

A good amount of refactoring and moving functions/structures around was
necessary to reuse zap local notification logic. I also attempted to
make the notification generation process more consistent between zaps
and other notifications, without changing too much of existing logic to
avoid even more regression risk.

General push notifications + local notifications test
-----------------------------------------------------

PASS

Device: iPhone 15 Pro simulator
iOS: 17.0.1
Damus: This commit
Setup:
- Two phones running Damus on different accounts
- Local relay with strfry-push-notify test setup
- Apple push notification test tool

Coverage:
1. Mention notifications
2. DM notifications
3. Reaction notifications
4. Repost notifications

Steps for each notification type:
1. Trigger a notification (local and then push)
2. Ensure that the notification is received on the other device
3. Ensure that the notification is formatted correctly
4. Ensure that DMs are decrypted correctly
5. Ensure that profile names are unfurled correctly
6. Click on the notification and ensure that the app opens to the correct screen

Result: PASS (all notifications received and formatted correctly)

Notes:
- For some reason my relay is not receiving zap events, so I could not
  test zap notifications yet.

- Reply notifications do not seem to be implemented yet

- These apply to the tests below as well

Changelog-Added: Zap notification support for push notifications
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
Signed-off-by: William Casarin <jb55@jb55.com>

DamusNotificationService/NotificationExtensionState.swift

@@ -14,6 +14,8 @@ struct NotificationExtensionState: HeadlessDamusState {
     let muted_threads: MutedThreadsManager
     let keypair: Keypair
     let profiles: Profiles
+    let zaps: Zaps
+    let lnurls: LNUrls
     
     init?() {
         guard let ndb = try? Ndb(owns_db_file: false) else { return nil }
@@ -25,5 +27,15 @@ struct NotificationExtensionState: HeadlessDamusState {
         self.muted_threads = MutedThreadsManager(keypair: keypair)
         self.keypair = keypair
         self.profiles = Profiles(ndb: ndb)
+        self.zaps = Zaps(our_pubkey: keypair.pubkey)
+        self.lnurls = LNUrls()
+    }
+    
+    @discardableResult
+    func add_zap(zap: Zapping) -> Bool {
+        // store generic zap mapping
+        self.zaps.add_zap(zap: zap)
+        
+        return true
     }
 }