ndb: make NostrEvents immutable

Since we can't mutate NdbNotes, let's update the existing codebase to
generate and sign ids on NostrEvent constructions. This will allow us to
match NdbNote's constructor

damus/Models/HomeModel.swift

@@ -821,10 +821,8 @@ func process_metadata_profile(our_pubkey: String, profiles: Profiles, profile: P
     }
 }
 
+// TODO: remove this, let nostrdb handle all validation
 func guard_valid_event(events: EventCache, ev: NostrEvent, callback: @escaping () -> Void) {
-    guard ev.id == hex_encode(calculate_event_id(ev: ev)) else {
-        return
-    }
     let validated = events.is_event_valid(ev.id)
     
     switch validated {