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/Views/Onboarding/SuggestedUserView.swift

@@ -8,13 +8,13 @@
 import SwiftUI
 
 struct SuggestedUser: Codable {
-    let pubkey: String
+    let pubkey: Pubkey
     let name: String
     let about: String
     let pfp: URL
     let profile: Profile
 
-    init?(profile: Profile, pubkey: String) {
+    init?(profile: Profile, pubkey: Pubkey) {
 
         guard let name = profile.name,
                 let about = profile.about,
@@ -64,7 +64,7 @@ struct SuggestedUserView_Previews: PreviewProvider {
     static var previews: some View {
         let profile = Profile(name: "klabo", about: "A person who likes nostr a lot and I like to tell people about myself in very long-winded ways that push the limits of UI and almost break things", picture: "https://primal.b-cdn.net/media-cache?s=m&a=1&u=https%3A%2F%2Fpbs.twimg.com%2Fprofile_images%2F1599994711430742017%2F33zLk9Wi_400x400.jpg")
 
-        let user = SuggestedUser(profile: profile, pubkey: "abcd")!
+        let user = SuggestedUser(profile: profile, pubkey: test_pubkey)!
         List {
             SuggestedUserView(user: user, damus_state: test_damus_state())
         }