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/Images/ProfilePicImageView.swift

@@ -62,7 +62,7 @@ struct NavDismissBarView: View {
 }
 
 struct ProfilePicImageView: View {
-    let pubkey: String
+    let pubkey: Pubkey
     let profiles: Profiles
     let disable_animation: Bool
     
@@ -90,12 +90,10 @@ struct ProfilePicImageView: View {
 }
 
 struct ProfileZoomView_Previews: PreviewProvider {
-    static let pubkey = "ca48854ac6555fed8e439ebb4fa2d928410e0eef13fa41164ec45aaaa132d846"
-    
     static var previews: some View {
         ProfilePicImageView(
-            pubkey: pubkey,
-            profiles: make_preview_profiles(pubkey),
+            pubkey: test_pubkey,
+            profiles: make_preview_profiles(test_pubkey),
             disable_animation: false
         )
     }