refactor: add Pubkey, Privkey, NoteId string aliases

This is a non-behavioral change in preparation for the actual switchover
from Strings to Ids. The purpose of this kit is to reduce the size of
the switchover commit which is going to be very large.

damus/Models/FollowersModel.swift

@@ -9,11 +9,11 @@ import Foundation
 
 class FollowersModel: ObservableObject {
     let damus_state: DamusState
-    let target: String
-    
-    @Published var contacts: [String]? = nil
-    var has_contact: Set<String> = Set()
-    
+    let target: Pubkey
+
+    @Published var contacts: [Pubkey]? = nil
+    var has_contact: Set<Pubkey> = Set()
+
     let sub_id: String = UUID().description
     let profiles_id: String = UUID().description
     
@@ -24,14 +24,13 @@ class FollowersModel: ObservableObject {
         return contacts.count
     }
     
-    init(damus_state: DamusState, target: String) {
+    init(damus_state: DamusState, target: Pubkey) {
         self.damus_state = damus_state
         self.target = target
     }
     
     func get_filter() -> NostrFilter {
-        NostrFilter(kinds: [.contacts],
-                    pubkeys: [target])
+        NostrFilter(kinds: [.contacts], pubkeys: [target])
     }
     
     func subscribe() {