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/Components/InvoiceView.swift

@@ -9,7 +9,7 @@ import SwiftUI
 
 struct InvoiceView: View {
     @Environment(\.colorScheme) var colorScheme
-    let our_pubkey: String
+    let our_pubkey: Pubkey
     let invoice: Invoice
     @State var showing_select_wallet: Bool = false
     @State var copied = false
@@ -108,7 +108,7 @@ let test_invoice = Invoice(description: .description("this is a description"), a
 
 struct InvoiceView_Previews: PreviewProvider {
     static var previews: some View {
-        InvoiceView(our_pubkey: "", invoice: test_invoice, settings: test_damus_state().settings)
+        InvoiceView(our_pubkey: .empty, invoice: test_invoice, settings: test_damus_state().settings)
             .frame(width: 300, height: 200)
     }
 }