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/Events/EventShell.swift

@@ -10,11 +10,11 @@ import SwiftUI
 struct EventShell<Content: View>: View {
     let state: DamusState
     let event: NostrEvent
-    let pubkey: String
+    let pubkey: Pubkey
     let options: EventViewOptions
     let content: Content
     
-    init(state: DamusState, event: NostrEvent, pubkey: String, options: EventViewOptions, @ViewBuilder content: () -> Content) {
+    init(state: DamusState, event: NostrEvent, pubkey: Pubkey, options: EventViewOptions, @ViewBuilder content: () -> Content) {
         self.state = state
         self.event = event
         self.options = options